This is on another Camaro that I own.. 91 Camaro RS 3.1L V6 5sp 373's.

When I fire up the engine, it idles right around 2,500 to 3,000. After about 5 minutes It will "Sometimes" idle down to near 1,500. The car drives ok, but the high idle drives the car for me, no need to press the accelerator for in town driving. It seems to be running ok, no misfires. Engine runs great other than the idling issue.

Any thoughts?

 

timing?


also, an option might be to adjust you tps

 

Massive vacuum leak is all that comes to mind...

 

+1 to all of it....though if the vacuum leak is too big the idle will come back down and the car will hiccup and stumble.

Definitely check for vacuum leaks with a can of TB cleaner or the like.....and make sure your throttle isnt sticking and the stop screw is properly set

 

I am having the same. exact. problem!! Car drives for me.. usually can drive about 39mph or 30.. somewhere around that.. kind of like cruise control. It happened after I took off my bellows and sprayed some throttle body cleaner into the TPI. I haven't found the solution yet. I am doing a search. I think someone else had this problem and it had to do with the IAC. I have a 89 5.7lt. I posted more information here:

https://www.thirdgen.org/forums/tpi/...y-cleaner.html

 

Sounds like the IAC is stuck-open and allowing extra airflow around the throttlebody...

 

Thats exactly what it is. The IAC is stuck. I am going to see about finding a replacement.

 

I found this link.. I might try it tomorrow
Tech Articles - Cleaning Your IAC

 

should I be able to push the valve in? I put some force on it but it doesnt move. I had some gunk in the springs.. not sure if that matters. Anyway I need to get a new one because I dropped mine and it did the "Triple Lindy" through the engine bay.

 

I was unable to push in the spring on mine too, although I am not sure if you are supposed to be able to. I was thinking about taking the one off my other Camaro and see how that one works, maybe even do a quick swap and see if it fixes the problem.

 

my 305 Lg4 does the same but except it stays around 2500

 

Perhaps the minimum idle air is set way too high. Also, a vacuum leak at the same level of the MAP sensor will not cause rough idle. It will just cause high idle. Unless it it is a serious vacuum leak the IAC should be able to control it. Only a vacuum leak below the MAP sensor will cause rough idle.

edit: Just noticed you had a v6. High min idle air setting will still do the same thing, but a vacuum leak will kill your idle since you have a MAF sensor.

 

How do you adjust this setting?

 

There's a stop screw behind the throttle plate, but the factory puts a cover over it that you have to knock out. If the cover is still there, dont screw with it cause it hasn't been tampered with...and I believe your TPS sensor is non-adjustable, therefore when you go messing with the min air, you cant recal the TPS voltage so you start seeing things like hanging or surging idle.

Try cleaning your IAC or swapping it first....and dont try to push it in or anything like you mentioned, its attached to a stepper motor, you can screw it up doing that. Dont wrestle it just clean it and get all the carbon off....your goal is to keep it from sticking. If the motor's damaged there's no fix except for a new valve.

 

Ordered my new IAC.. was like 70$ at AdvancedAuto. Should arrive tomorrow. I am not really expecting this to fix my problem- I am thinking it might have something to do with a vacuum leak since all my hoses are shot. I dont remember touching any hoses when I took the snorkle off and sprayed the TB with TB cleaner.. but could have.. anyway, that moment was when the idle went crazy

 

Poop, that didn't fix it... as I was guessing it wouldn't.. but I was really hoping that it would! Checked my hoses and they _look_ ok. I disconnected the PVC and had good succion on the hose.. I didnt use a guage to test it.

The new IAC seems more robust. I had to screw the nozzle down just under 1-1/8" . Now when I start the car it jumps to 3k rmp and slowly goes down to 2k.

TB blades seem to move freely.

1 thing to note about the IAC is that it says you can reset it on TBIs. Just drive around 40mph and it will tell the IAC pin/nozzle thing to fully extend and seat inside the tb. Unfortunatly, I have a TPI and that trick didnt work Hmm, I wonder if they gave me the wrong one.. I doubt it. Hmm, nope.. correct part.

Not sure what other things I can do except take it to the shop.. damn.. I just got it painted and I wanted to drive around for my birthday

 

Is there a solution for this? I have found at least 4 different threads dealing with high idle, but no solutions have been posted. It's my turn to deal with this, and it would be nice to find that someone has figured it out.

1985 Firebird, 2.8L V-6, 5 Speed.

Idling at 2500 rpm with the IAC simply not moving. Can the Mass Airflow Sensor (MAF) cause this??

 

If it's idling that high, I'd be surprised if there wasn't a vacuum leak.

*edit* And... Holy smokes this is an old thread.. I was even more amused by the fact that I essentially had the same response almost 8 years ago..

 

I see plenty of vacuum leak pointers, but nothing that has actually solved the problem has been posted...anywhere.

We have chased vacuum leaks, replaced and reset the IAC, and replaced and adjusted the TPS. We hook up the WinALDL software and watch the IAC start at zero counts (~1000 rpm) and slowly "control" the idle speed up to ~2250 at 79 counts. The odd thing is that the IAC just camps out at 79 counts and stays there. Rock steady with no variation. It's like it just gives up.

The factory cap is still in place on the "minimum air" screw, so we haven't messed with that. The throttle blade bushings seem to be tight. This is the 2.8l V-6 engine.

Thanks for chiming in. Any ideas? Lots of people seem to have this problem, but it's frustrating when no solutions have been shared.

 

I would try to verify your grounds--I believe there is a primary ground that goes to the back of the cylinder head on the passenger side. Other than that perhaps try another ECM?

 

There's one I haven't thought of. I will check that the next time the car is here. My son is driving it and he shows up once or twice a week. Thanks for the pointer!

 

Here's the latest thing. The IAC goes to 130 counts when the key is on, but engine not running. When you start it up, the IAC starts to come down and control the idle speed. Within a few short seconds, it gives up. The IAC stops moving at random count numbers. I saw 60, 75, 30 as examples. It seems like the ECU decides the engine is not idling and abandons the IAC where ever it is at that moment. The idle speed creeps up to ~2200 RPM, the IAC doesn't move, and the MAF doesn't seem to register increased airflow as the RPM increases. The MAF does register increased airflow as the throttle blade is opened, so it seems to function on some level.

Here's the question of the day: How does the machine know when it's idling?

We replaced the TPS very recently, but it is now erratic and shows 0.00 volts most of the time. Any help or guidance is GREATLY appreciated.

1985 Firebird, Stock 2.8 V6, 5 Speed, New tune up (plugs, wires, cap, rotor (we didn't change the points this time...) Timing is dead on 10* BTDC)

 

I have had this problem on couple engine and have found bad seat in behind IAC carbon fouled the seat and was bad enough it had wore groove in seat

 

Carl, Is there a fix for the bad seat (other than replacing the throttle body)?

 

I have heard of people drilling them out and putting brass seat in I've always replaced it

 

I am having high idle issues as well - 91 305 TPI 5-speed. I can adjust the idle by entering service mode, waiting long enough for the IAC to fully close, unplug IAC, turn off key, remove AB jumper, start engine, adjust idle by adjusting TB set screw, turn off engine, plug IAC back in. Car typically runs fine on first drive idling down nicely when out of gear or just idling. Once I shut her off and drive her again she seems to want to idle high when I come to a stop. She typically will settle down but often surges a few hundred RPM's. Any ideas? I have replaced both the IAC and the TPS. No vacuum leaks found.

 

Same exact issue here, will test for vacuum leaks but if that does not solve the issue I will try with a rebuilt ECM from BSE.

 

Would EST be a thing to check?
IIRC, you can only see your real idle speed while the EST connector is open, so maybe you set your minimum idle to a value that has already been influenced by the ECM.
That would be a variable thing that changes from one startup to the next.
The rest of the procedure with the IAC and so on seems golden to me.

 

Corrected my idle issue by replacing the coolant temp sensor. Used an AC Delco part rather than a cheap Amazon part. Easy 2 minute fix that corrected about 95% of the idle issue. Occasional fluctuation I chalk up to a tired old original 305.