specialized

Hi Fellas. This is my first post, although I've been reading post and tech articles on this site for a long time - a lot of great info here.

I've been working on the elusive "idle issues" that these cars seem to have for a few weeks on this '89 I purchased a couple months ago. I've read all the post and Tech articles I can find on here about the issue.

What I've done - cap, rotor, plugs & wires, ohm'ed injectors, replaced CTS, replaced IAC, replaced fuel filter, replaced air filter, cleaned MAF, verified fuel pressure, set timing, checked for vacuum leaks, cleaned throttle body, verified and adjusted TPS, set minimum air via procedure outlined here, checked for ECM codes (there are none).

My issue - I can set minimum air via the procedure. After I remove diagnostic jumper, reconnect IAC and start car, it works great. Idles good, drives good, idles responds good when going into gear, or turning AC on, etc. I can drive the car and it runs strong. As soon as I turn the car off, and immediately restart it, I'm back to 2100 - 2200 RPM idle. It's like as soon as I turn it off, it looses track of the IAC or something?

What's next?

Bob88GTA

iTrader: (2)

WOW, seems like you covered quite a bit. Try this....Start car. Is it idling at 2k like you say? Push on the throttle lever back. does idle drop? Another thin....take boot of an look into the TB and move throttle by hand. Is the butterflies going all the way closed?
Just a few more things to check. You MAY be sucking ait at the TB Shaft bushings, which in turn would deliver more air and cause a high idle. My bet is you got a sticking shaft/butterfly plates.

specialized

Thanks Bob88GTA - I'll try that tonight. My only thought is, if this is the case, why would the car be idling perfectly, simply shut it off and restart without touching anything and then go right back to 2200 RPM? If it was sucking air somewhere, why would an ignition cycle change that?

Bob88GTA

iTrader: (2)

IDK, something is telling the IAC to retract and let more air in. I thought the same thing. How long does the idle stay up? Does it ever come down?

specialized

It doesn't seem to come down, but I've only let it run a couple minutes. This morning I started it up after sitting all night. It started off about 1500 - 1600 RPM. After it ran a few seconds and the temp started to come up, I could hear the tone change of the air being sucked in, so I assumed that was the IAC opening up, it then rose to that 2200 RPM range.

One other note, I'm pretty sure the butterflies are not closed all the way at idle, because when setting minimum air, I noticed that they had to be open a little to get the required idle characteristics outlined in the procedure.

Bob88GTA

iTrader: (2)

OK, well there it is. I'm really close to that IAC/TPS procedure. When you start the procedure, you want that minimum idle screw backed out as far as you can. The engine will darn near die on you....will sound like its going to stall. THEN go from there and start that procedure all over again. It might take a few times, but you will get it. One other note of advice....when you go to start it with the IAC disconnected, you may need another person to go out and turn the Minimum Idle Screw so it will idle. Without the second person, you'll have to try it, get out and turn the screw a tad, and repeat.

specialized

I've done it with the screw all the way out and had to do the "jump in and out of the car" thing to get it to idle at all. During the procedure, I've read a couple different versions in regard to removing the jumper on the ALDL after disconnecting the IAC - one says to turn the ignition off to remove the jumper and one says to leave it in. What's your opinion?

Bob88GTA

iTrader: (2)

I don't remove it until I turn the engine off and reconnect the IAC Plug, then remove jumper, Start car and then drive it for about 20 minutes for the "re-learn" process.

specialized

Interesting...I've read that starting the car with A-B jumpered can damage the ECM...

Bob88GTA

iTrader: (2)

I go by this one and Vaders, never had a problem

https://www.thirdgen.org/tpimod2/

specialized

Yep - those are the two I've been using, just wasn't 100% sure when to remove the jumper as it doesn't specifically say. I'll try it your way tonight. If the butterflies do indeed end up needing to be "open" a little to get the car to idle while setting minimum air, could that be pointing to another issue of some kind?

Bob88GTA

iTrader: (2)

IDK....Here's some good reading

TPS and IAC.html

Bob88GTA

iTrader: (2)

Did you take off the IAC housing and clean all that carbon out of the passages when you did the TB???

specialized

Yeah - I cleaned the IAC passages too. Thanks for all of your input, I really appreciate it. I think I'll go through the minimum air procedure again tonight and pay closer attention to where the blades are when the idle is set correctly. I still just has me believing that it's something electrical since it will behave correctly, turn the car off and restart and it's wrong again. Seems like it's "losing" something when turned off.

Bob88GTA

iTrader: (2)

understand. Scan tool and software would show your IAC counts and if it was getting signals from TPS and computer.

Good luck!

specialized

I've been thinking about a scan tool. I've never used one. Can a person make adjustments with them, for example, to the IAC count? Any recommendations as to brand/model for a back yard mechanic?

specialized

Update - I went through the minimum air procedure again last night. This time I did a couple things differently. I left the jumper in when I started the car after unplugging the IAC. I noticed that the SES light flashed code 12 and then went to constant fast flashing, which I thinks indicates closed loop? I adjusted the minimum air screw way up before starting the car. So when I started it, it was idling around 1500 rpm. I slowly backed the screw out until the car would barely idle, it finally coughed and quit. I turned the key off, pulled the jumper and plugged the IAC in. Started the car and idle was correct. Drove around for 20 minutes at under 40 mph, car stalled a couple times at stops. After 20 minutes it idled fine. I could shut it off and restart it and it idled good. Progress it would seem. I let the car sit for 2 hours and tried it again. Started it up and back to 2100 RPM! uugggghhh

Youngs92

iTrader: (1)

My camaro is doing the same thing, but mine will sometimes start with the idle high, but will also randomly rise when the car is running. For example, I stopped at a light with the clutch in idle was fine at 700 RPM, then it suddenly rose to 1500 and as I drove, worked its way to 2000. That to me sounds electrical, but I've gone through everything you have done with no luck.

Youngs92

iTrader: (1)

Not sure if you are still having issues, but I would suggest you check the throttle body gasket for leaks. If you use carb cleaner to do this, be sure to protect your painted surfaces.

I also thought by TPS was good because I could set it to the proper value, but it's the small changes in resistance as the throttle body opens that can't easily be seen with a voltmeter that'll show if it's good or not. For $40-50, I would swap it anyway.

86IROCZ28NDC

Hey has anyone found out a solution to this high idle bs, I've tried everything on my 86 camaro and seems like nothing is working. Please help if you have a solution

Fred SS

iTrader: (3)

To the op, seems you have tried everything, but have you tried replacing the ecm? Maybe you can borrow one from a friend. Seems like the ecm is not keeping the re-learned data after the motor is turned off.

TT 68

I know, old thread but I just saw this and had a similar problem with my 91 Z/28. Turned out the circuit board inside the ECM case had come loose and would occasionally ground out against the case. This would put it into limp home mode with the high idle. Hit a bump or make a turn and it would return to normal.

Seth James

Good morning!!
I have 91 firebird that I have swapped everything from a 91 z28 into. The problem I’m having is no communication with a scan tool. Car runs fine just can’t communicate with module. Anyone run into this?

Tuned Performance

iTrader: (92)

No communication is kinda a sign that the ecm is bad.
can you even blink codes ?
If you need a 1227730 I have a few $55 shipped in the states.
was this a tbi to tpi swap ?

FFormula350

Hello "tuned performance " I would be interested in an Ecm. How can I contact you to tell you details.
Thank you

Tuned Performance

iTrader: (92)

Pm sent

BlackFall

Has anyone come up with the reason for the IAC Motor to keep clicking with KOEO ?

Also the TPI issue I was having with the Engine Idling up was My EGR would trigger to open and the diaphram had a leak, vacuum leak allowed to much air in and she jumped in RPM.

Another car my EGR was sticking and full of carbon. So I cleaned it and put a screen between two gaskets to prevent it happening again.

Another car I built . I was in a different state when I heard there was a serious problem that the car would idle up to 4k + rpms and they had another mechanic play with it. He replaced the... Distributor, TBI, MAF, PROM, ETC... So they called me and flew me up .. I walked in, at this part the car would not start , VATS was triggered, when I got it to fire by bypassing VATS.. it was codes and rpm through the roof...

I looked at the TB and noticed a piece of plastic road debris stuck in the throttle.. pulled it out, idled great... Other problems.. I had a custom prom and the yellow plug ecm, that were now gone.. I had removed vats with the other prom so now it had a random vats in there and wrong prom that didn t match the engine build, among other issues from someone not starting at simple inspection... they threw parts at it until they ruined the engine.. The worst issue was metal on the dipstick ... When they changed the distributor.... they didn't know this engine runs roller valve train , roller cam.... are distributor can gear... I just had to throw that One in.

There was also the time I was given a car because they left a shop rag in the engine.. I replaced 3 lifters and picked every piece of rag out of every part of th e engine and it ran great.

Now I'm babbling...

What else would cause the AIC to keep kicking , KOEO ? The wires to the IAC actually show a cycling signal to them...

Bill1992

Thank you so much for this post. 5 minutes and I fixed a problem that's plagued me for a while now. I just got the car a month ago and I got rusty on troubleshooting engines. What I couldn't figure out, aside from bad idle, was the vac line that goes from tb to breather would kill it when hooked up. I'm not sure how it ties in to the iac but I cleaned the iac and it's hole and runs and idles like a champ now. Thanks!
edit: i put this on the wrong thread somehow. I was resonding to "how to clean iac" oh well.