high idle

[Jarek5_7]

I have high idle , around 1100 or little more rpm.

on datamaster desired idle is 650. recently I changed plenum gaskets, injectors, coils, spark plugs and wires because there was a problem with ingnition, miss etc. now the only problem left is high idle.
(oh maybe not the only:) but most annoying)

I`ve read that tps v should be from 0.54 to 6v
mine at idle are around 0.24v

other thing is how to check iac?
datamaster shows that iac is 0 on idle , whem I rev a little it goes to 30 and them falls to 0, with it rpm falls but now as low as I wanted it to be.

is the a way to check iac? or to calibrate it?

[XfireZ51]

The fact that the IAC count is 0 at idle suggests that there is bypass air
present. Does idle drop to 700 or so if you stab the pedal?
Did you move TPS? With scantool in place, move throttle from closed to open and back
Does it feel smooth? Do volts seem to hang or move in a abrupt or choppy manner?

[Jarek5_7]

the idle dont drop even below 1000.

I dodnt move tps. volts from tps move smoothly.

what do You mean by bypass air present?

is 0 the middle position for IAC? is the middle position for iac the required position to maitain idle (650) rpm?

by bypass air present you meant the air bypass by half opened aic?

[Demps]

First thing I would check (since you just performed work) is the hose under the throttle body. You can see the "L" shaped fitting pointed aft from the driver's side under the TPS-->get a small flashlight and mirror. If not attached, you will have a high idle. Sometimes you can attach it without removing the plenum again. The rubber hose has a compression-type clamp on it.

Also, the TPS is adjustable and should read correctly.

Ted

[Jarek5_7]

It had high idle before the work I did. I think I know about which hose you r talking about, I think its in place, but I`ll check it again.

so what v should tps at idle have? 0.54?

[XfireZ51]

Jarek,

0 steps for IAC means it's completely closed. Outside air is getting in some other way. Throttle plates may be opened too far or there's an air leak.
Loosen TPS and set it to .5v with scantool connected. You'll do that with
ignition on, motor off.

[tpepmeie]

First thing I would check (since you just performed work) is the hose under the throttle body. You can see the "L" shaped fitting pointed aft from the driver's side under the TPS-->get a small flashlight and mirror. If not attached, you will have a high idle. Sometimes you can attach it without removing the plenum again. The rubber hose has a compression-type clamp on it.

Also, the TPS is adjustable and should read correctly.

Ted

I'm with Ted... the canister purge hose under the front driver side of the plenum is likely disconnected, which will cause the massive air leak = high idle. That was the first troubleshooting I did on my '91 back in 1999.

[XfireZ51]

I'm with Ted... the canister purge hose under the front driver side of the plenum is likely disconnected, which will cause the massive air leak = high idle. That was the first troubleshooting I did on my '91 back in 1999.

He mentioned that it had a high idle even before he did the plenum removal.
So whatever is causing high idle hasn't been affected.
Surprising he 's not getting code for LO TPS V.

[Pete]

Basicly you have a vacuum leak.

I spray a mist of water around the gasket and vacuum ports/hoses if the idle starts to fluctuate you found your vacuum leak,good luck.

You need to adjust your TPS to .55
You need to have 10-20 IAC counts at idle.

Pete

[Jeffvette]

I`ve read that tps v should be from 0.54 to 6v
mine at idle are around 0.24v



Correctly set your TPS, and I think you will find the high idle will go away.

[Jarek5_7]

I set up tps to 0.55v and started the car. after couple of secs idle went down and fell to around 900, I waited adn when the car got hotter I reved it a little couple of times , when it went to closed loop mode idle even got higher adn stayed around 1000, but they are little lower then earlier.

the iac stayed 0, so I think it has a leak somewhere.

I was searching and after engine shutdown I heared some little sucking noise around the back of the engine. I checked hose to fuel pressure regulator and to brake booster , they are ok.

I unplugged the hoose that goes from pcv valves into front part of plenum at the driver side and ended the hose with duct tape to see whats gonna happen. now after starting the engine had around 700 rpm and idled smooth.

so faulty pcv valves? ( I dont know how this pcv ventilation works, just trying to find some diagrams of its connections in the car.)

[XfireZ51]

Ah yes. Sounds like you need the old tie wrap around the upper and lower PCV hoses. I had that same issue when I first got my 92. It was very slight but Mr. Haibeck pointed it out to me.:hello:

[Maxlean]

Correctly set your TPS, and I think you will find the high idle will go away.

How's that? 0 IAC counts means it can't bring the idle down any lower regardless of what tps is. I agree with the others that there is a vacuum leak somewhere (or possibly a miss adjusted base idle screw).
Scott

[Jeffvette]

How's that? 0 IAC counts means it can't bring the idle down any lower regardless of what tps is. I agree with the others that there is a vacuum leak somewhere (or possibly a miss adjusted base idle screw).
Scott


TPS, at the incorrect voltage will cause a high idle. He has two issues going on, and needed to make the correction of the proper TPS voltage. THe idle did go down, but still not enough.

I agree he does have a vacuum leak, and probably several small ones on the PCV system at either the PCV valves or the Side connection of the plenum for the PCV and Fuel Evap lines.

[Jeffvette]

(or possibly a miss adjusted base idle screw).


You should never ever adjust the base screw. That was set by Rochester and never adjusted by MM when the motors were run. Moving this screw just masks the real issue.

[Jarek5_7]

I checked pcv rubber hoses, they are ok, everything clamped with steel screw clamps, pcv valves from up side were wrapped around with electric isolation tape because the part which goes to the rubber hose was loose in this hoose. so I changed this tape for new one and make sure it sits tight in this hoose also I put two plastic tie wraps to hold rubber hose+pcv valves+rubber hose in vertical.

that really made a diffrence after starting the car rpms were lower, I drove a mile to my friend and let it idle until fans turn on, it idlet great on low rpms.

while I drove back my foot was little heavier on the accelerator, but reasly road is slippy and I didnt floor it or anything. after stop rpms were annoying high, around 2k slowly falling, I stopped engine, and start it again, rpms falled to 1k.

so any ideas where to look?

one think is the 1k idle and the other is how long it takes for rpm to fall to this 1k level after stop, is it the issue with 1990 chip and only new chip can help?

[XfireZ51]

Jarek,

One thing to try is pulling out IAC and cleaning the pintle and the orifice in the throttle body. They tend to "carbon up" not allowing IAC to close completely even though it says it is commanding 0 steps. Throttle plates may be sticking a bit also. See if you can clean those a bit.

[Jarek5_7]

when I took of plenum I also replaced tb gaskets and cleaned iac, but I didnt even look at the orifice in tb, I clean it and iac once again.

btw, I was reading the board and couple of people mantioned a "black goo" in the planum sealing the tb plates. what is it actually and can it be the cause of high idle?

mhm I just thought about something. maybe I`ll start the car with iac out to see if its moved smootly, of course plug the tb hole with something.

[Nick]

btw, I was reading the board and couple of people mantioned a "black goo" in the planum sealing the tb plates. what is it actually and can it be the cause of high idle?
Its called dag, and the lack of it can cause a high idle condition. Haibeck has a fix for it if the dag is missing, and you send him your TB. He worked wonders on mine by doing some other "adjusting."

[Jarek5_7]

can anyone tell what does he do with the tb ? maybe he puts some sealant there? I`m from europe so sending tb to him would take a lot of time....

I bought a new iac valve, :D, at my friends car parts store, he had it on a shelf, ;) lots of cars uses this iac.

http://img147.imageshack.us/img147/8352/20090121020yk6.th.jpg (http://img147.imageshack.us/my.php?image=20090121020yk6.jpg)

I swapped the iac and drove a little. while car is still idles ok sometime 700 sometime around 900-1000, thats not to bad, but when I`m driving it it idles way to high ~1500 rpm, this is really annoying because car doesnt slow down by itself how it should do and for example while reaching lights or some stop and in gear I have to slow it down by breaking more ( the engine pulls a little). its very annoying because even after stop it revs high too long and rpm drop slowly, to slowly to drop to correct rate while stopping or slowing down in normal traffic.

I dont have any fault codes. I`ve been looking for vacuum leak all over. I`ll do it again.... but can it be the 1990 prom issue ? would a custom chip solve the problem? or does anyone have the changes in prom which were made in newer chip for 1990? so I could make those changes on my own by tunerpro or some other software? thanks guys!

[XfireZ51]

Jarek,

So after you swapped IAC, you say that it idled fine until you drove it? Did you go thru the IAC reset procedure? Any chance you could scan during your drive?

[Jarek5_7]

yes it idles fine until driven. I swapped the iac and tried to reset it as in the book I have. its " corvette fuel injection and electronic management" by charles o. probst. it covers many efi on corvettes also zr1. its written there to press accelerator pedal a little and start the car for 5 sec then turn off the ignition for 10 seconds. I did that and havent notices any change. but now I see that its also written there that the reseting of iac is needed after unpliging the iac while engine is runing. I didnt unplug it on engine runing.
I will do that tommorow and then the reset procedure. Or I should reset it a diffrent way? also I will try to scan the car while driving tommorrow.

I really want to get this car into a good condition and high idle is I think the most annoying issue in it.

So far I changed for new injectors, plenum and tb gaskets, coils, wires, plugs, checked for vacuum leaks, havent found any yet.
( sec vacuum pump is working and sec vacuum system holds vacuum good, also the actuators hold vac and works good, the primary vacuum reservoir hold vac, I check also vac on the other side in the hose going to plenum it also holds vac)

[Jarek5_7]

if after I drive the car the ecm wants to have good idle rpm like 650 but engine idles high, its a vacuum leak for sure right?

maybe some egr valve or something is turn on and it leaks vacuum after a drive?

[Nick]

Marc Haibeck makes several adjustments to the linkage and replaces the dag with a spray-on compound. He fixed my high idle TB and its been great for several thousand miles and several years. Once you have sorted out all of the other potential issues (and it sounds like you have), I'd give him a call and see what he says. :thumbsup:

[WydGlydJim]

Just a note. The 90s are notorious for having a slow return to idle. I've read it can take up to 30 seconds. This is an eternity, if you have ever clocked it. Plus the idle will not come all the way down while the car is rolling, even if the clutch is in and off the gas. Just making sure you are not chasing a problem that is not there. Many people complained about this issued, and a new prom was calibrated. Mine will come down, but sometimes at a light, it will not come down all the way, before the light changes.

[WB9MCW]

Just a note. The 90s are notorious for having a slow return to idle. I've read it can take up to 30 seconds. This is an eternity, if you have ever clocked it. Plus the idle will not come all the way down while the car is rolling, even if the clutch is in and off the gas. Just making sure you are not chasing a problem that is not there. Many people complained about this issued, and a new prom was calibrated. Mine will come down, but sometimes at a light, it will not come down all the way, before the light changes.

:thumbsup:

Marc Haibeck makes several adjustments to the linkage and replaces the dag with a spray-on compound. He fixed my high idle TB and its been great for several thousand miles and several years. Once you have sorted out all of the other potential issues (and it sounds like you have), I'd give him a call and see what he says.

Now I see why you have the other post ging for where to get a stock prom --- As you will see in my answer to you on that thread ---HAIBECK is the man for the chips!!!:cheers:

[Jarek5_7]

can anyone post here a vacuum routing schematics?

I found only this one http://www.zr1netregistry.com/gifs/vacuum.jpg

but I cant see for example where secondary map should be conected ?

[tomtom72]

The part labeled Vacuum differential sensor is the part we all call the secondary MAP sensor. The hose feeding it comes out of the left side of the plenum between the front four & rear four runners, if I remember correctly. That MAP is bolted under the bracket that the ECM and cruise control diaphram is mounted on, just on top of the battery.

:cheers:
Tom

[Jarek5_7]

I thought ith was the differential sensor but I got confused because I was looking for a sensor with two inlets. differencial as for measuring difrence in pressures. mine isnt connected to anything :/

[WB9MCW]

The part labeled Vacuum differential sensor is the part we all call the secondary MAP sensor. The hose feeding it comes out of the left side of the plenum between the front four & rear four runners, if I remember correctly. That MAP is bolted under the bracket that the ECM and cruise control diaphram is mounted on, just on top of the battery.

:cheers:
Tom

And often a backfire will blow that MAP hose loose causing a high idle:thumbsup:

[WB9MCW]

I'm with Ted... the canister purge hose under the front driver side of the plenum is likely disconnected, which will cause the massive air leak = high idle. That was the first troubleshooting I did on my '91 back in 1999.

This was an early post in the thread that was telling you of this common problem :thumbsup:

[WB9MCW]

He mentioned that it had a high idle even before he did the plenum removal.
So whatever is causing high idle hasn't been affected.
Surprising he 's not getting code for LO TPS V.

But a pointed out here this does not seem to be your issue.

Perhaps it is the PROM chip thing.

For those of us lucky to live close to Haibeck a simple drive to his shop and review would be the key to success.

You may want to email him and have him read this thread and work with you to solve your issues IMO.

He would know best what to try next and get you to an ultimate solution.:thumbsup:

That is why he is the ZR-1 specialist. No one knows em like Haibeck does as many will attest too.

Now there are others who are also very good with the ZR-1's like SGC and DRM not to slight them at all. Or Jeff at PNW ZR-1.

But I like to support those who advertise here >> http://zr1netregistry.com/index.htm

or like Jeff who is on the forum here all the time with advise etc.

We support those who support us. :thumbsup:

[Jeffvette]

And often a backfire will blow that MAP hose loose causing a high idle:thumbsup:

Wrong MAP sensor.

[WB9MCW]

Wrong MAP sensor.

OK you know I thought it did not sound like the right one.

At any rate I'll let you tell em which one :thumbsup:

[Jarek5_7]

I hooked up the secondary map corectly and checked all the vacuum hoses, changed check valves. Now the secondary system works! and car pulls great, I think I still has a little vacuum leak but I think its from pcv valves, I will have those new in couple of days and we`ll see when I replace them.

aslo I changed pilot bearing because of tranny noise, luckly as me and Bill Boudreau / zfdoc.com (which send me a long email with some advice) thought the source of tranny noise was the pilot bearing. Now the zf6 doesnt produce any noise and is really quiet.

[WB9MCW]

Hey J your getting there buddy!

Good to hear your rolling now a pulling hard:cheers:

That is great that Bill took the time to email you and help out -- good guy that Bill-- He goes the extra yard for ZRONERS :thumbsup:

[tomtom72]

On the PCV valves.....I bought new top F shaped connector and new injector housing connectors back in 05. I installed them and they worked great for awhile. Now I just gave up and bought the expensive SAMCO replacement PCV top and bottom hose set from LIMEY.

I do believe if you use the car enough that the amount of oil blow by in our PCV system degrades the rubber PCV parts made from standard rubber in a fairly short time so that they start to leak slightly. As time goes by they degrade progressively and the small leaks become bigger & bigger & bigger.

This is JMHO. The only thing I know for sure is that the new rubber connectors were tight up to about a yr ago. They don't seem to last long.

:cheers:
Tom