Further idle diagnosis....

[Roadster]

So I been having this slight idle problem since January. More annoying than an actual problem. But something I can live with for now...

As mentioned in another thread when I start the engine (has Marc's chip) if revs high for a few seconds and then come down to 650-700 r's at idle. Driving out of the development and stopping along the way, the idle comes back down to the 650-700 range. Now when on the road going through the gears and then coming to a complete stop the idle can sometimes be around 900-1000 r's. Now what I don't understand is that with my foot on the brake and I let up on the clutch pedal, I can get the engine to drop to the lower rpm range and stay there. On further stops it can be a hit or miss situation on where the idle will be, unless I use the same procedure as mentioned.

Talking to Yun, as he mentioned it could be the shaft in the throttle body that may be worn. Also did the airhorn test and used the FSM as my block in front of the airhorn. At high idle 900-1000 r's after blocking the airhorn, the idle came down to normal after about 3-4 seconds. And on Marc's site it also mentions the problems with the TB. So a lot to absorb.
I also cleaned (sprayed) the outside throttle springs and whatever part of the shaft I could get to with WD40. Amazing the amount of grime that ended up on the paper towels. I also sprayed lightly inside the TB, even though it isn't recommended per Marc's papers. Didn't really matter, because it acts the same. I always start off with a normal idle and even revving the engine to around 1500-2000 rpm's the engine will come back down to normal. Now when driving, it is a different result.
Hooked up the Tech 1 on a warm engine and the IAC was reading about 20 with normal driving. Backing off in 3rd gear @ 2000 r's, the IAC would be much higher and fluctuate at higher readings. Come to a complete stop whether the idle is normal or higher, reading has always been "0".
From Marc's site:
"When the IAC goes to zero the idle speed can not be reduced by the engine control system. Then the engine idles at more than 650 rpm." What I don't understand is when the idle is normal, I still get the "0" IAC reading when stopped.

TPS is set @.54v And the throttle stop screw is adjusted correctly. The throttle cable has play, so it isn't too tight that it would hold the throttle off of the idle stop. I changed the IAC from before, but it did not make a difference. I need to verify that the IAC fully closes as per Marc's papers.
Other then the above the engine runs great especially with the secondaries fully operational.

So short of sending out the unit to Marc for a rebuild, guess I will keeping trying to find an easier if possible fix...

[secondchance]

There is an idle set screw (throttle plate stop) that can be adjusted. We might try backing off a bit. Worth a try...
Also, giving it another thought, blocking the air horn maintaining 650 may be due to just enough air leakage somewhere other than the TB.

[XfireZ51]

So I been having this slight idle problem since January. More annoying than an actual problem. But something I can live with for now...

As mentioned in another thread when I start the engine (has Marc's chip) if revs high for a few seconds and then come down to 650-700 r's at idle. Driving out of the development and stopping along the way, the idle comes back down to the 650-700 range. Now when on the road going through the gears and then coming to a complete stop the idle can sometimes be around 900-1000 r's. Now what I don't understand is that with my foot on the brake and I let up on the clutch pedal, I can get the engine to drop to the lower rpm range and stay there. On further stops it can be a hit or miss situation on where the idle will be, unless I use the same procedure as mentioned.

Talking to Yun, as he mentioned it could be the shaft in the throttle body that may be worn. Also did the airhorn test and used the FSM as my block in front of the airhorn. At high idle 900-1000 r's after blocking the airhorn, the idle came down to normal after about 3-4 seconds. And on Marc's site it also mentions the problems with the TB. So a lot to absorb.
I also cleaned (sprayed) the outside throttle springs and whatever part of the shaft I could get to with WD40. Amazing the amount of grime that ended up on the paper towels. I also sprayed lightly inside the TB, even though it isn't recommended per Marc's papers. Didn't really matter, because it acts the same. I always start off with a normal idle and even revving the engine to around 1500-2000 rpm's the engine will come back down to normal. Now when driving, it is a different result.
Hooked up the Tech 1 on a warm engine and the IAC was reading about 20 with normal driving. Backing off in 3rd gear @ 2000 r's, the IAC would be much higher and fluctuate at higher readings. Come to a complete stop whether the idle is normal or higher, reading has always been "0".
From Marc's site:
"When the IAC goes to zero the idle speed can not be reduced by the engine control system. Then the engine idles at more than 650 rpm." What I don't understand is when the idle is normal, I still get the "0" IAC reading when stopped.

TPS is set @.54v And the throttle stop screw is adjusted correctly. The throttle cable has play, so it isn't too tight that it would hold the throttle off of the idle stop. I changed the IAC from before, but it did not make a difference. I need to verify that the IAC fully closes as per Marc's papers.
Other then the above the engine runs great especially with the secondaries fully operational. And when stutting down the engine there is no pre-ignition at the higher rpm range, which is a good thing.

So short of sending out the unit to Marc for a rebuild, guess I will keeping trying to find an easier if possible fix...

How do you know that the Min Air Adjustment is correct? With a 0 IAC, sounds like it isn't.

[Roadster]

There is an idle set screw (throttle plate stop) that can be adjusted. We might try backing off a bit. Worth a try...
Also, giving it another thought, blocking the air horn maintaining 650 may be due to just enough air leakage somewhere other than the TB.

I did see that but did not make any adjustments. I imagine I'll make a mark on it to keep track of any adjustments made. I checked all of the hose connections that I could get to and always make sure any screw seen is tight.

How do you know that the Min Air Adjustment is correct? With a 0 IAC, sounds like it isn't.

I don't know, but if it is out of adjustment then why after starting the engine the idle will be normal or close to normal and not at the 900-1000 range?

[Roadster]

Ok, just looked up one of my previous threads dated 12-21-16 where I used the Tech 1 for the first time.
Here are a the results from those readings....


It will ask you for the 8th digit of your VIN#, which is "J" and will then ask you if a 94 Corvette. Press "YES" and you are in.....
The Menu....
F0....DATA LIST
F1....FIELD SER
F2....DTC
F3....SNAPSHOT
F4....MISC TEST

Started with F0, these results are with the engine running.....

ENG SPEED
870-890......as engine warmed up......830-815 rpm's
DESIRED IDLE
850.............as engine warmed up......812-800 rpm's

Engine coolant reading is off by 2 degrees from the IP with the tech 1 giving a higher reading by that amount.

MAP (KPa,V)
39 1.50-1.54-1.56

FUEL EVAP PURGE
0%

THROTTLE POS
0.52 VOLTS increased as throttle was depressed slightly .62 VOLTS
THROTTLE ANGLE
0%................................................ .............................2%

LEFT H025 BNK 1
53 mV
LOOP STATUS
OPEN LOOP

RIGHT H025 BNK 2
44-53 mV

ST FUEL TR BNK 1
128
LT FUEL TR BNK 1
115

FUEL TRIM CELL
16 CELL
FUEL TRIM ENABLE
NO

SPARK ADVANCE
12 degrees MPH 0 km/h 0

KNOCK RETARD
0
KNOCK SIGNAL
NO

SYSTEM VOLTAGE
14.1 VOLTS
FUEL PUMP VOLTS
13.5 VOLTS
EGR DESIRED POS
0%
EGR ACTUAL POS
0%
EGR PINTLE POS
0.60 VOLTS
EGR DUTY CYCLE
0%

IDLE AIR CONTROL
22
ENGINE SPEED
678-700 RPM's

FAN 1
OFF
FAN 2
OFF
A/C FAN REQUEST
NO
A/C REQUEST
NO
A/C CLUTCH
OFF
AIR PUMP RELAY
OFF
AIR CONTROL
DIVERT

MPH
0
Km/h
0

1-4 SHIFT ACTIVE
NO
ENG OIL TEMP
153 degrees by tech 1........149 degrees by IP
SEC VAC (kPa, V)
0 0.58

POWER SWITCH
NORMAL.....w/key turned....FULL
SECONDARY SYSTEM
OFF
FEDS/PASSKEY
OK
SEC AIR INLT SOL
OFF

CALIBRATION ID 9011

ENGINE SPEED @200degrees
691 RPM's
DESIRED IDLE
662 RPM's

After totally warmed up received these readings.....

LEFT H025 BNK1
as low as 75 mv to as high as 735 mv
LOOP STATUS
CLOSED LOOP

FUEL TRIM CELL
16 CELL
FUEL TRIM ENABLE
YES

Notice the IAC and idle readings warming up to full operating temps.
It appears that the idle may have not always been at the 650 range, but it was never at the 900-1000 range either.
So something changed after the plenum pull one month after these readings. It has to be a minor adjustment or minor vacuum leak, I just can't wrap my head around that the throttle shaft would develop that much play to increase the idle at times in one month.

[XfireZ51]

Why did u pull the plenum?

[Roadster]

Why did u pull the plenum?

Found out that I had various vacuum leaks. Figured if we're under there, just do it all and be done with it. And the funny thing about it is, that even with the vacuum leaks, I never had a problem with the idle, go figure!!!
All of the items were completed....
1-to get secondaries fully operational
2-replace starter
3-replace coils
4-replace vacuum lines
5-replace check valve
6-replace filter
7-replace PCV valves
8-replace PCV connectors
9-replace MAP connector
10-replace Fuel Regulator hose
11-clean the valley
12-unclog the drain
13-clean Plenum and other parts
14-replace Fuel Injectors
15-replace alternator
16-changed spark plugs at a later date

I have to say the engine runs great, and I thought it was great before. What did I know??? Once the idle issue gets sorted out, it will be perfect for me. The only future mod I would do is the exhaust when the time comes.

[Roadster]

Been giving the idle issue some thought, spoke to a relative over the weekend who is into heavy equipment for a livelihood and at one time had a performance oriented business years ago.

This is his theory....
He doesn't feel that it is a vacuum leak or the throttle body shaft for the following reasons. If it was a vacuum leak, then the idle would be higher all of the time and not just some of the time. As mentioned before, when I first start the engine after it comes down off high idle, it is around 650-700+ r's. When driving it will either stay the same when completely stopped or be around the 900-1000+ r's. And when I put a load on the engine, with me completely stopped, foot on the brake, in 1st gear and letting up on the clutch pedal, the r's drop down to 700+ rpm's and stay there until the next complete stop. Then the idle will be back up to 900-1000 rpm's. And yes the IAC is @ 0 when stopped. His feeling is that the TPS may be defective. Saying that when you first start the engine and on restarts your idle is normal, or somewhat normal. In those situations the TPS is sensing all of what is should for the correct idle. When you drive and are coming to a complete stop, the TPS goes through "steps" as the engine de-accelerates and may not be sensing that last "step" it needs to sense for the proper idle, when completely stopped. But again, if you shut the engine down and then restart, the TPS is fine. He also feels that if it were the throttle shaft, you would not be able to get the normal idle during restarts.

Now that is just his thoughts and it does make sense to an extent. So your thoughts are welcome on this issue, and very much appreciated.:D

Also took my wife out today along with the Tech 1 so she could record some of the readings during our ride.

Here they are.......I also have Marc's chip as mentioned....

Start-up...cold engine
Desired idle...850 rpm's.............Actual idle...890 rpm's
IAC 25

Engine warming up with temp @135*
IAC 2-1-0....................idle 695 rpm's

All other reading were with the engine at normal operating temps.

During our ride the IAC would be 0 @idle and would jump up during acceleration and de-acceleration from 5-11-16-18-14-15-17-29-23-47-42-5-0
The numbers would increase during acceleration and slightly change when shifting, but liked to be around 16-17 in the 2700-3100 rpm range.
When backing down is when you would see the higher 47-42 and sometimes higher than that (as high as 90-87-85) depending on the speed when backing down.
Then when coming to a stop the count would decrease and be @ 5 then 0 when completely stopped.

Even when the engine speed @idle was as high as 1125'r's the TPS was still @.54v

MAP (KPa,v)
36 1.36-1.40

TPS @ all idles .54v
Throttle Angle 0% @idle

LHB 1 Closed Loop
range from 98-750 mV

RHB 2 Closed Loop
same as above

ST Fuel Trim Bank 1...122
LT Fuel Trim Bank 1....126

Fuel Trim Cell......16 cell
Fuel Trim Enabled.....Yes

Spark advance......9-10* and in the high 20's when accelerating

When engine speed was @850's during idle, the desired idle was listed as 662 r's

When shutting the engine down, and key off the Tech 1 read IAC 135 and engine speed was @ 884 r's. Don't know if this reading has any meaning or value.

Upon hot restart the idle was @740r's and the IAC @ 0


I did replace the IAC as mentioned before after the plenum pull. And I know that it is possible for more than one part to go bad or a newer part to be deflective. I have been there done that before with other vehicles....lol

I also want to add that the idle stop screw did not move at any time one way or another during regular or high idle stops.

Took pics with the engine running and @ normal and high idle, you would think that at high idle if the blades were opened slightly that the idle stop would not fully make contact, no so as shown in the pic, it was the same for both idles...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170418_122209.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170418_122209.jpg.html)

[XfireZ51]

If there is no "hunting idle", the IAC count is 0 because the bypass air is being introduced thru the throttle plates and not the IAC. Close the plates, and the IAC count will increase. U will need to reset or at least recheck the TPSv whenever you do that. Everything else u logged is normal and accountable for in the calibration.

[Roadster]

If there is no "hunting idle", the IAC count is 0 because the bypass air is being introduced thru the throttle plates and not the IAC. Close the plates, and the IAC count will increase. U will need to reset or at least recheck the TPSv whenever you do that. Everything else u logged is normal and accountable for in the calibration.

Ok, a few simple questions......

1- I am assuming that I can use the Tech 1 since it reads the voltage when I reset the TPS, therefore eliminating the use of a mutimeter, correct?

2- are you saying to adjust the idle stop nut & thread and make sure the blades are completely closed?
From what I can determine, they are!!! And wouldn't normal idle suggest that they are fully closed?

3- The idle has never "hunted" but has not always been rock steady according to the Tech 1, it does fluctuate 30 to 40 rpm difference whether normal or higher idle.

4- Can you explain more that if the IAC is 0 and my idle is normal, then how can air still be introduced through the throttle blades as opposed to a higher idle which would seem more logical?

5- Then if the IAC count increases as you start off and accelerate, does that mean the IAC is working properly at that time and allowing the proper amount of air into the TB?

Thanks for any additional info......appreciated........:)

[secondchance]

When there is no vacuum leak, wouldn't closing off air coining in through the air horn stall the motor?

[Roadster]

When there is no vacuum leak, wouldn't closing off air coining in through the air horn stall the motor?

If there is some type of vacuum leak, wouldn't the high idle be there all of the time, and not as what I am experiencing?
When I did that test on Friday with the air horn blocked at high idle, it came back down to normal after about 3-4 seconds, and engine continued to run and stayed at normal idle with the air horn then unblocked.

So the choices I have so far.....
1-recheck throttle plates for closure.
2-recheck TPS
3-recheck IAC
4-should I re-torque the plenum bolts?
5-would the rear bracket alternator bolt right next to #2 injector be a factor if not torqued down correctly? Although I did make sure it was tight when reinstalling the alternator.

Just got back from a short ride, on start-up engine idle was normal, and even my first two stops at low speed. Once I reach a higher speed, and then stop, it is with the high idle. It has never been at high idle 900-1000+ during any cold, or hot restart. The high idle only happens when driving the vehicle.

And let's assume that the throttle shaft is the problem, then why when at the higher idle (900-1000 r's) would the idle then come down to 650-725+ r's when I am putting a load on the engine as I am letting up on the clutch pedal with no accelerator movement at all? That is telling me that the throttle blades have not moved as I am not touching the accelerator. And wouldn't the idle stop "thread" be off the stop if the throttle body blades were opened or moved during the higher idle?

[secondchance]

If there is vacuum leak, I suspect pig tail PCV hose to plenum and not plenum to IH. Leak can be intermittent.
Mt experience with TPS failure was worn out spot resulting in a dead spot. This type of failure results in stumbling as throttle is opened gradually.
Now that I think about it, closing off air horn should completely cut off air intake stalling the motor. Fact that rpm drops to 650, suggests air leaking into intake somewhere. Number 1 suspect is the pig tail PCV hose.

[Roadster]

Reading the FSM Book 2, I am learning quite a bit, especially on the Tech 1 and the range for the parameters being read. Also has a TECH 1 DATA DEFINITION section, very informative.

I also may have damaged my IAC because I did move the pintle, which you should not do according to the info I am reading. Although the IAC seems to work fine otherwise. I also did not measure the distance between the tip of the pintle and the mounting flange when installing. Also did not reset the valve pintle position as per the FSM.
I will check into PCV hose pig tail.

From the FSM Book 2....
"IDLE AIR CONTROL - Range 0-255 - Displays the commanded position of the idle air control pintle in counts. The higher the number of counts, the greater the commanded idle speed. Idle air control should respond fairly quickly to changes in engine load to maintain desired idle RPM."

Right now the only way my IAC responds from "0" @ idle is when the vehicle starts in motion, then it responds quickly and starts to record 5 and up as speed increases.

In the listing for TECH 1 DATA,
"Idle / Upper Radiator Hose Hot / Closed Throttle / Neutral / Closed Loop / Acc.off"
The above is required for the values listed in the FSM during idle.

Learning more and more to be learned.....

[Roadster]

Went back out to the garage, thinking and retracing all of our steps during the plenum pull. Can't think of anything that we left out except, we did not change the air horn to TB gasket. We felt it looked good and left it alone.
Now the problem of the higher idle started as we were doing our test drive after everything was back together. So I'm thinking about that gasket. Just now took the air horn off and I think it was and is time to change it.
Also disconnected the IAC for a measurement, the FSM states that if the distance of the pintle extension is greater than 28mm, use finger pressure to slowly retract the pintle. 28mm equates to 1.1023622 inch (1 3/32') and my measurement was 28.58mm or an 1 1/8 inch (1.13 Inches ) to be technical. Used finger pressure to retract the pintle and now measures under one inch as shown in the pic. Also need to lube the O-ring with engine oil, which I did not do previously.
And will follow the instructions as per FSM...
"Tighten to 27 lb. in.
Reset the IAC valve pintle position
A. Depress accelerator pedal slightly
B. Start and run engine for five seconds
C. Turn ignition "OFF" for ten seconds
D. Restart engine and check for proper idle operation"

Will do this later in the AM and hopefully with some other minor items, things will be normal.
Now with the throttle blades I did notice some "dirt" on the secondary blades, the primary blade looks fine. I worked the linkage and the primary blade closes right up to the indent in the TB where it is supposed to be. There is no way to adjust it more than what it already is now. That being said, as you can see in the pics, there is some buildup around the secondary bore(s) and I don't think that is some dag. Not sure, but I feel it shouldn't be there, it could also be from some of the WD40 spray I used the other day.
Will also address that later this AM.
And is there any type of sealer used on the air horn side of the gasket, or do you install dry?

So will try these things first and go for a ride. Hopefully this will cure the sometime higher idle. If not will look into the pigtail that Yun suggested.

Removing the gasket...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170418_233118.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170418_233118.jpg.html)
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170418_234123.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170418_234123.jpg.html)
just about cleaned and ready for the new gasket. anyone know what these numbers would mean on the back of the air horn???
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170418_234218.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170418_234218.jpg.html)
the TB...take note of the butterflies and the residue around them...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170418_234353.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170418_234353.jpg.html)
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170418_234435.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170418_234435.jpg.html)
the pintle after retraction...I know the tape measure is not flush against the base, but placed it there to give you an idea....the pintle is now under one inch when adjusting the tape measure for the difference...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170419_001242.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170419_001242.jpg.html)

[Paul Workman]

Just checked my IAC and it is reading 33 @ idle, temp at 215ºF, rpm 750. If your IAC is going to ZERO at idle, then it is no longer controlling idle speed. So, either the idle air setscrew is holding it the primary throttle plate open to far, or there is another source for air.

That IAC ZERO reading at idle is something to run to ground before anything else, me thinks...

[Roadster]

Just checked my IAC and it is reading 33 @ idle, temp at 215ºF, rpm 750. If your IAC is going to ZERO at idle, then it is no longer controlling idle speed. So, either the idle air setscrew is holding it the primary throttle plate open to far, or there is another source for air.

That IAC ZERO reading at idle is something to run to ground before anything else, me thinks...

Just got back from a ride, finished everything mentioned above, thought I had success, but no go!!! It was fine for the first 5 complete stops, then started up again. IAC was up when first started but then came back down to "0" when stopped. If you rev the engine, the IAC reacts immediately. Also at high idle when stopped and when letting off the accelerator coming to a stop, the Throttle angle was 0% any time my foot was off the throttle, as per the Tech 1.
TPS @any idle and again with foot off the accelerator was .54v.
I was going to reinstall my old IAC, but I think it is toast, can't even move the pintle. I might go buy another and see what happens....

Can you further explain "reading at idle is something to run to ground before anything else, me thinks"

thanks.....

[Roadster]

Can it be possible that the IAC is defective? Although it registers on the Tech 1, the counts are allover a wide range when driving. Sometimes it holds in one area, other times it varies constantly from mid teen counts to as high as in the 80's and 90"s
Should the count be constant in different rpm ranges?

Sent from my SM-G935P using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[XfireZ51]

You mentioned that u blocked airhorn when high idke, and that idle came down and stayed down after unblocking the airhorn. That tells me ur throttle blades are sticking a bit open for a reason. When u block the airhorn, it causes a vacuum that draws the throttle blades in and therefore reducing the amount of air entering the plenum. Idle drops. Move the throttle again, and the blades return to original position.

[Paul Workman]

Can you further explain "reading at idle is something to run to ground before anything else, me thinks"

thanks.....

Sorry to confuse the issue! :p "Running (a problem) to ground" is just an expression, meaning to resolve (that particular) problem completely.

I find especially when a problem is or appears to be complex that in the discovery of symptoms phase, several "clues" turn up: some causal, some resulting from a cause(s). Divide and conquer!!, often I've found it is helpful to attack the one symptom at a time, rather than being distracted by a host of anomalies (the IAC = zero, in this case).

The IAC counts should NOT be going to ZERO at idle, is (to me) a glaring error! It says (to me) that even with the IAC (air) cut off, the motor continues to run at excessive rpm and sometimes fluctuates as well. that indicates the motor is getting air - excessive air - not to put too fine a point on it. Anything from the IAC itself to a gasket leaking or throttle blades not closing* completely...something is amiss.

Divide and conquer! Blocking off the air-horn tightly with a flat surface, like a (hard-back) book, should kill the motor. If doing so does NOT kill it, the problem, or most of it, is after the TB; not the throttle plates or IAC or whatever. But, if blocking kills the motor, that suggests the issue is isolated to a source w/in the TB.

And, before I forget, When coming down to a stop from highway speed, my 90 will be at a fast idle for a few seconds before returning to normal idle. Be sure to let it do so. But, in addition, should for any reason the motor stall while the car is rolling, upon restart while still rolling, it will hang at a fast (2000 or so) rpm until I bring it to a complete stop. Then it will settle to a normal idle and behave. Again, mine is a 1990, and these quirks are typical, I've come to understand: nature of the BEAST.

[Roadster]

I can understand what you are saying, but what I don't understand is why the throttle angle is always at 0% at high or normal idle. Wouldn't that indicate that the blades are completely closed?
I appreciate all the comments and suggestions, but it looks like another plenum pull is in order to make sure everything has stayed attached. Could be that there is a slight vacuum leak. Not sure as you and many others have way more experience than I do with the LT5.
Will have to wait for now as I'm out at the 74....alot of work to be finished here..lol


Sent from my SM-G935P using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[Roadster]

Not sure if this will have any bearing on my idle problem or not. The vacuum pump is for the secondary operation if I understand that correctly. Just did a test with the key on and the pump came on for about 4 seconds. Then as is the pump came back on after 20 seconds for a split second. Then each time the pump came back on, it was a 1/2 second difference lower. I let it happen about 4 times and it was down to about an 18 second difference. So I imagine that there is a vacuum leak in the system. Is that a correct assumption???
Thanks for any additional info.....

[tpepmeie]

I can understand what you are saying, but what I don't understand is why the throttle angle is always at 0% at high or normal idle. Wouldn't that indicate that the blades are completely closed?

The ECM doesn't actually measure the throttle angle as "zero". Rather it sets as zero the lowest voltage registered by the sensor at various intervals. In other words, it assumes the lowest voltage, say .52v, is closed throttle and therefore sets that as zero. It is updated from time to time, but frankly without my notes, I can't remember the exact logic.

I think the suggestion that the throttle plates might be hanging slightly open, then get shut by the extra vacuum when the TB is blocked off, might be the most likely. Can you re-do the blocked off TB test when the idle is high? Just to check where the air source is (TB or after).

[Roadster]

The ECM doesn't actually measure the throttle angle as "zero". Rather it sets as zero the lowest voltage registered by the sensor at various intervals. In other words, it assumes the lowest voltage, say .52v, is closed throttle and therefore sets that as zero. It is updated from time to time, but frankly without my notes, I can't remember the exact logic.

I think the suggestion that the throttle plates might be hanging slightly open, then get shut by the extra vacuum when the TB is blocked off, might be the most likely. Can you re-do the blocked off TB test when the idle is high? Just to check where the air source is (TB or after).

Thanks for the explanation. I just thought that since the Tech 1 was reading the Throttle Angle @0% and showing .54v for the TPS at any idle and anytime my foot is off the accelerator that the blades would be fully closed.
So if what you and others have suggested about the throttle blades, would a possible solution be to undo the idle stop and make sure the blades are fully closed, then adjust that stop to that position???
When I had the air horn off to change the gasket, there did not appear to be any additional area to where the blades could be adjusted more closed than what they already are...but I imagine it's worth a try.
Won't be able to do the test for a day or two, but will do it again.
Have to find a different book, as it almost sucked in my FSM.....lol

[tpepmeie]

It's likely not the stop screw if it can actually idle down to normal. If it's sticking it's in the mechanism (shaft or blades) my guess.


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[Roadster]

It just doesn't feel like the blades or the shaft are sticking, as throttle response is non-existent. When first starting the engine or doing a hot restart and revving the engine with normal idle, it returns down to normal.
If the throttle is or was sticking, then why would it not stick on a restart after shutting down the engine with a high idle? If the throttle is sticking then wouldn't it still be sticking at high idle on the restarts, which it never does?

[Paul Workman]

Ya gonna have to TEST your theories. Can't assume anything[-X; only trust what you VERIFY!

PS:

Because the vacuum pump does shut off, and you're not reporting any codes/secondary issues, the check valve to the plenum IS working. Your Idle problem is NOT coming from the SPT system.

However, besides gaskets, there ARE several other vacuum circuits that could be introducing air into the plenum. You might want to verify the MAP vacuum is not leaking, and then block off the other plenum vacuum circuits, e.g., the purge line, PVC line...see what happens when these other "blank checks" are eliminated...

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/plenumvacuumcircuitsLT5LargeLarge.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/plenumvacuumcircuitsLT5LargeLarge.jpg.html)

[XfireZ51]

Take a strip of paper and stick it between the primary throttle plate and bore. Pull it through. Is there any drag? Do it also after opening the throttle.

[tpepmeie]

Do I understand right that the high idle occurs after you've been into the throttle a good bit? I thought I saw that earlier somewhere in this thread. If that is the primary symptom then would point me towards the larger throttle plate mechanism hanging up. The 59 (or. 63mm) bores don't open up under light throttle. It's a progressive linkage.... the small primary plate opens at the first several degrees of throttle position.


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[conesare2seconds]

Fwiw, I had a high idle after the engine was warm. Marc found the throttle blades were hanging up. Had him recondition the throttle body.

[Roadster]

Ya gonna have to TEST your theories. Can't assume anything[-X; only trust what you VERIFY!

PS:

Because the vacuum pump does shut off, and you're not reporting any codes/secondary issues, the check valve to the plenum IS working. Your Idle problem is NOT coming from the SPT system.

However, besides gaskets, there ARE several other vacuum circuits that could be introducing air into the plenum. You might want to verify the MAP vacuum is not leaking, and then block off the other plenum vacuum circuits, e.g., the purge line, PVC line...see what happens when these other "blank checks" are eliminated...

Will go through all that you have suggested. Makes sense to check all of the vacuum circuits before anything else.

Take a strip of paper and stick it between the primary throttle plate and bore. Pull it through. Is there any drag? Do it also after opening the throttle.

I will try the paper test.

Do I understand right that the high idle occurs after you've been into the throttle a good bit? I thought I saw that earlier somewhere in this thread. If that is the primary symptom then would point me towards the larger throttle plate mechanism hanging up. The 59 (or. 63mm) bores don't open up under light throttle. It's a progressive linkage.... the small primary plate opens at the first several degrees of throttle position.

Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

Yes it does occur after I'm into the throttle, but sometimes it's not so much that it would start to bring on secondary operation. And if the larger throttle plate mechanism is hanging up, then why doesn't continue to hang up after a hot restart? I guess I'm having a hard time thinking its the throttle blades. And I know anything is possible.

Fwiw, I had a high idle after the engine was warm. Marc found the throttle blades were hanging up. Had him recondition the throttle body.

That will be the last resort, it's just unusual it happened just like that!!!


Thanks again for all of the replies.....appreciated......:)
Won't be able to further check things until Sunday. Going out to the 74 again tomorrow, and getting some additional help from a car friend.

[DRM500RUBYZR-1]

Tom,
Just a thought.
You might want to isolate the cruise control and ASR units and controls from the equation to make sure that they are not in any way restricting or affecting the return to idle.
Of the two, the cruise has both vacuum and mechanical interaction.
Perhaps during re-assembly somehow they were jostled.
While vacuum seems to be your gremlin, rule out as much else as is possible.
GL, you will get it!
P.S.
We have a smoke machine if you need to keep looking for vacuum leaks.
Give a call and stop by with some coffee and donuts, and I'll have the guys hook it up.
:cheers:
Marty

[XfireZ51]

This is one of those cases where Occam's Razor applies and yet we keep looking for the more complicated explanations.

[DRM500RUBYZR-1]

This is one of those cases where Occam's Razor applies and yet we keep looking for the more complicated explanations.


Those Franciscan's never shaved; They thought it too complex!
:cheers:
Marty

[Hib Halverson]

Couple of observations....

If the IAC counts are zero for a sustained period, given a properly functioning IAC and that the TPS is set correctly, you likely have a vacuum leak somewhere. It can be anywhere in the intake tract, even the TB shafts.

The secondary pump and the port throttle don't affect a problem like this because they are downstream of the TB.

What I'd lke to see if the long term fuel trims for both sides at idle.

I would not use the minimum air adjustment as a bandaid for this problem. In factd, if you've already changed that as a "fix", you've created more of a problem you have solved.

I'd first readjust the throttle stop screw, then start your diagnosis from there.

[Roadster]

I have found the source of the problem, a big thanks to everyone who has replied. :D
And I stand corrected big time.....the problem is the primary throttle blade.
Here is how the determination came about......
Following the advice from Paul, to check everything out...
Doing the paper test that Dominic suggested...
Giving more thought to what Todd mentioned about the throttle blades...
Also more thought about what conesare2seconds said about his idle...
And also to VetteVet who I spoke to on the phone along with Yun for all of the insight given.....:cheers::cheers:

But is was Marty that put me over the edge......lol when he mentioned the smoke machine, I remembered that there is one out at the garage where the 74 is residing. So I grabbed it today and took it home, a good move.

Marty, thank you sir.....I will still come down and pay you a visit and will gladly bring the coffee and donuts.....and a big thank you for the offer to use your smoke machine, when I read it, the light bulb went off....:cheers::-D

Set up the machine, took off the brake booster line on the plenum and hooked up my own configuration of hoses to connect to the open port. Took off the air duct and covered up the opening of the throttle body with a plastic bag. Turned on the machine and there are no leaks coming from under the plenum or any connections on the top of the plenum. But and a very big but is I noticed that the plastic bag over the throttle would expand. I undid the plastic bag and looking directly into the air horn I could now see the steam coming from what I thought was the passenger side throttle plate. Then I realized that there was still an opening that had the be blocked off from inside the air horn. Now doing the test again, the steam is now coming out of the bottom of the primary blade, and nowhere else. Did this test 3 times and the same results. Also did the paper test that Dominic suggested and it did pull through, the first time it was tight, but when I redid the test after moving the throttle, it pulled through a number of times.
So there you have it, I was very hard headed....lol thinking that it cant be the primary throttle blade and that is exactly what it is.....now I know the problem....here are a few pics of the process.....

I had these hoses for years and years without ever using them, today they came in handy for the fog machine...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170422_162111.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170422_162111.jpg.html)

[Roadster]

my hose configuration...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170422_162504.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170422_162504.jpg.html)
the plastic bag...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170422_162457.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170422_162457.jpg.html)
you cant see the steam, but it was coming out the bottom of the primary blade.....
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170422_165151.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170422_165151.jpg.html)

[conesare2seconds]

:thumbs up:

[Roadster]

Couple of observations....

If the IAC counts are zero for a sustained period, given a properly functioning IAC and that the TPS is set correctly, you likely have a vacuum leak somewhere. It can be anywhere in the intake tract, even the TB shafts.

The secondary pump and the port throttle don't affect a problem like this because they are downstream of the TB.

What I'd lke to see if the long term fuel trims for both sides at idle.

I would not use the minimum air adjustment as a bandaid for this problem. In factd, if you've already changed that as a "fix", you've created more of a problem you have solved.

I'd first readjust the throttle stop screw, then start your diagnosis from there.

I have not or attempted to adjust anything. I would imagine that since I found the primary blade to be leaking the fog during the test that I should adjust the throttle stop screw as you mentioned to start with.

I understand that the secondary pump has nothing to do with the problem, but felt I should report everything that I have noticed with the entire system.

I would have to do another Tech 1 test for the latest Fuel Trim info. Previous results are in post #8 unless you have already seen them.

[XfireZ51]

Couple of observations....

If the IAC counts are zero for a sustained period, given a properly functioning IAC and that the TPS is set correctly, you likely have a vacuum leak somewhere. It can be anywhere in the intake tract, even the TB shafts.

The secondary pump and the port throttle don't affect a problem like this because they are downstream of the TB.

What I'd lke to see if the long term fuel trims for both sides at idle.

I would not use the minimum air adjustment as a bandaid for this problem. In factd, if you've already changed that as a "fix", you've created more of a problem you have solved.

I'd first readjust the throttle stop screw, then start your diagnosis from there.

Hib,

Just a point of clarification, but if you are going to "readjust" the throttle stop screw, you would do that only to re-do the min air setting. And that is to adjust for the desired idle w the IAC steps sufficient to allow ECM idle control.

[Roadster]

So what would be the overall consensus moving forward? Is it futile to try an adjustment? Or is it a better idea to send the unit out to be redone???
Guess I leaning towards a last ditch effort to see if any adjustment(s) will work or not, before sending the TB out!!!

Also another thought and question. When I first started the engine the other day, IAC counts appeared to be normal but then came down to "0" after a few stops. So that would indicate to me that the throttle was completely closed at first start up. And when doing hot restarts, although the idle would be what I consider "normal", the IAC still remained at "0". And since the "fog" tests points to the primary blade leaking, I imagine even with the idle normal, and the rpm's fluctuating somewhat, that would still indicate that the primary throttle is not completely closed, correct??? And that would also explain why the idle varies anywhere from 25-45, 50 rpm difference which I am considering to be in the "normal" range. And also why the IAC count is still "0" as opposed to the higher range as when the vehicle starts in motion, correct???
Just trying to get a better understanding of the operation of how and why!!!
Opinions, thoughts.....

[XfireZ51]

So what would be the overall consensus moving forward? Is it futile to try an adjustment? Or is it a better idea to send the unit out to be redone???
Guess I leaning towards a last ditch effort to see if any adjustment(s) will work or not, before sending the TB out!!!

Also another thought and question. When I first started the engine the other day, IAC counts appeared to be normal but then came down to "0" after a few stops. So that would indicate to me that the throttle was completely closed at first start up. And when doing hot restarts, although the idle would be what I consider "normal", the IAC still remained at "0". And since the "fog" tests points to the primary blade leaking, I imagine even with the idle normal, and the rpm's fluctuating somewhat, that would still indicate that the primary throttle is not completely closed, correct??? And that would also explain why the idle varies anywhere from 25-45, 50 rpm difference which I am considering to be in the "normal" range. And also why the IAC count is still "0" as opposed to the higher range as when the vehicle starts in motion, correct???
Just trying to get a better understanding of the operation of how and why!!!
Opinions, thoughts.....

There is a function named "Throttle Follower" where the IAC Opens and Closes in coordination w the throttle position. There are delays, and decay rates associated w that. So the variation in IAC opening is very normal. The IAC is usually the result of something not the cause. RPM variation can be due to a number of issues but that's another story.

[Paul Workman]

So what would be the overall consensus moving forward? Is it futile to try an adjustment? Or is it a better idea to send the unit out to be redone???
Guess I leaning towards a last ditch effort to see if any adjustment(s) will work or not, before sending the TB out!!!

Also another thought and question. When I first started the engine the other day, IAC counts appeared to be normal but then came down to "0" after a few stops. So that would indicate to me that the throttle was completely closed at first start up. And when doing hot restarts, although the idle would be what I consider "normal", the IAC still remained at "0". And since the "fog" tests points to the primary blade leaking, I imagine even with the idle normal, and the rpm's fluctuating somewhat, that would still indicate that the primary throttle is not completely closed, correct??? And that would also explain why the idle varies anywhere from 25-45, 50 rpm difference which I am considering to be in the "normal" range. And also why the IAC count is still "0" as opposed to the higher range as when the vehicle starts in motion, correct???
Just trying to get a better understanding of the operation of how and why!!!
Opinions, thoughts.....

Well, the "take-away" from this is/was intermittent idle rpm AND THE IAC COUNTS GOING TO ZERO.

The ECM uses the IAC to control the idle; when the primary plate is "closed" (except for a tiny amount afforded by the idle set screw) and at idle there are some nominal IAC counts e.g., 10+ (depending), but NEVER ZERO under normal (static) conditions...EVER.

And, the evidence is bolstered by the idle was observed wandering out of control; going to ZERO is a classic clue that air might be getting in somewhere else; idle set-screw miss-adjusted, or a LEAK elsewhere.

Occam's Razor: A philosophy that states (in effect): when there are two possible reasons for an event, the simplest is usually the answer.

LOGIC is an essential tool in troubleshooting. But, until proven out, a logical assumption is just a hypothesis until it has been VERIFIED BY TESTING. Just about everyone who ever tried to solve a puzzling situation has been guilty of "over-thinking" the situation and assuming "if this, then that, and then..." without VERIFYING the "if this..." - the first logical assumption in the first place is where trouble begins.

[Roadster]

There is a function named "Throttle Follower" where the IAC Opens and Closes in coordination w the throttle position. There are delays, and decay rates associated w that. So the variation in IAC opening is very normal. The IAC is usually the result of something not the cause. RPM variation can be due to a number of issues but that's another story.

I don't mind the variation in the idle, as long as its the "normal" idle.
Interesting info...thanks....

Well, the "take-away" from this is/was intermittent idle rpm AND THE IAC COUNTS GOING TO ZERO.

The ECM uses the IAC to control the idle; when the primary plate is "closed" (except for a tiny amount afforded by the idle set screw) and at idle there are some nominal IAC counts e.g., 10+ (depending), but NEVER ZERO under normal (static) conditions...EVER.

And, the evidence is bolstered by the idle was observed wandering out of control; going to ZERO is a classic clue that air might be getting in somewhere else; idle set-screw miss-adjusted, or a LEAK elsewhere.

Occam's Razor: A philosophy that states (in effect): when there are two possible reasons for an event, the simplest is usually the answer.

LOGIC is an essential tool in troubleshooting. But, until proven out, a logical assumption is just a hypothesis until it has been VERIFIED BY TESTING. Just about everyone who ever tried to solve a puzzling situation has been guilty of "over-thinking" the situation and assuming "if this, then that, and then..." without VERIFYING the "if this..." - the first logical assumption in the first place is where trouble begins.

Also logical thoughts......appreciated....

I am thinking that the logical thing to do is reset the idle adjustment screw in very small increments as needed to see if the primary blade will close completely. And in between those adjustments (have pizza & a beer)....:)
take a test ride and then use the fog machine to verify whether or not the adjustments are having an effect.

[Roadster]

Take a strip of paper and stick it between the primary throttle plate and bore. Pull it through. Is there any drag? Do it also after opening the throttle.

Also did this test with the idle stop screw against the stop and at first there is a drag and difficulty pulling the paper through. Worked the throttle a few times and now the result is less drag and no real difficulty pulling the paper through.
So I am assuming that an adjustment is needed. Just have to figure out what size nut that is, as I think I can loosen the nut with a long ratchet wrench. I have a 5/16' that fits, but not snug enough. Just need to find out the actual metric size it really is.

[XfireZ51]

U really need to replace the stock stud w a hex bolt. I think its a 7mm bolt head. The stud uses a very small allen wrench that's nearly impossible to reach because it was never meant to be adjusted. However, after 25 yrs everything wears. There is a procedure that I have documented on the registry for re-setting the throttle plates for Min Air.
You will want to use a scanner to set throttle plate opening based on amount of IAC steps desired at idle. I use somewhere between 8-15 steps and do this with coolant at operating temps w fans on for the extra load. Whenever you adjust the throttle stop, it then is necessary to check TPS v and possibly re-adjust to read >.53v and <.57v.

[Roadster]

U really need to replace the stock stud w a hex bolt. I think its a 7mm bolt head. The stud uses a very small allen wrench that's nearly impossible to reach because it was never meant to be adjusted. However, after 25 yrs everything wears. There is a procedure that I have documented on the registry for re-setting the throttle plates for Min Air.
You will want to use a scanner to set throttle plate opening based on amount of IAC steps desired at idle. I use somewhere between 8-15 steps and do this with coolant at operating temps w fans on for the extra load. Whenever you adjust the throttle stop, it then is necessary to check TPS v and possibly re-adjust to read >.53v and <.57v.

What section on the registry is the documentation? And is it possible to do with everything still connected? So I can use the Tech 1 and I assume as I close the primary blade then the IAC counts will increase, correct?

[XfireZ51]

You'll want to check the General and Technical sections. Part of the procedure is blocking of the IAC airway and disabling the IAC motor.

[Roadster]

You'll want to check the General and Technical sections. Part of the procedure is blocking of the IAC airway and disabling the IAC motor.

For further info on Dominic's procedure for Minimum Air Idle Adjustment Thread
here is the link...

http://www.zr1.net/forum/showthread.php?t=27764

Thanks again for posting.....:thumbsup:

[Dynomite]

Just got back from a short ride, on start-up engine idle was normal, and even my first two stops at low speed. Once I reach a higher speed, and then stop, it is with the high idle. It has never been at high idle 900-1000+ during any cold, or hot restart. The high idle only happens when driving the vehicle.


When you completely stop the vehicle, how long will the high idle 900-1000 stay? Forever? a few minutes? a few seconds?

[Roadster]

When you completely stop the vehicle, how long will the high idle 900-1000 stay? Forever? a few minutes? a few seconds?

When first started and slightly warmed up, the first 2 or 3 complete stops are at "normal idle". Then after putting a slight or heavier load on the engine, the future complete stops would be at the high idle. And it would stay there forever, unless I turned the engine off and then did a restart, it would come back down to "normal". But on the very next complete stop it would once again be at high idle.

Now, as mentioned before this was after the first plenum pull. So apparently something was disturbed causing this issue.
As mentioned in my other thread, going to go over everything, install new plenum gaskets.
And also learned that the primary blade is not to be completely closed and that no "dag" was used on that blade.

Also brought to my attention that the lines I mentioned in the other thread concerning the connector are EVAP lines.
So maybe there was a loose connection in the one that came out real easy. I don't know, but hopefully will get all of this resolved.