Further idle diagnosis....

[secondchance]

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

[Roadster]

Originally Posted by secondchance

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...


just about cleaned and ready for the new gasket. anyone know what these numbers would mean on the back of the air horn???

the TB...take note of the butterflies and the residue around them...


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...

[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]

Originally Posted by 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...

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?

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[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]

Originally Posted by Roadster

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

thanks.....

Sorry to confuse the issue! "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.