I have a 1990 firebird 3.1L. I recently had to remove the plenum (upper and lower), including fuel rail and throttle body in order to change valve cover gaskets due to ever increasing oil leaks. Once I put everything back together, and hooked back up throttle body and connected IAC, the check engine came on and I got trouble code 35 (IAC).
I replaced the IAC with a new one just because I could tell the old one was original and cleared the code by disconnecting the battery for a few mins. When I start the car and let it idle for 15-20mins, everything is fine with no trouble code and idles at around 700rpm which is normal (timing at 10degrees per hood label).
When I drive it around for any given amount of time, whether 5 mins or an hour, once I stop and put it in park, within a couple of mins the idle jumps to 950-1000rpm and I get trouble code 35 again. Any help with this would be great. Thanks

 

TBH I am not sure if this is valid or not......

Some folks in this thread claim it is the real deal and has helped them. One guy claims it's bunk. I have no info as I do not have a 3.1 engine.

But, since it costs nothing to try, perhaps you could try this and see if it helps? (If anything, it certainly can't hurt ). If it does or doesn't work, please post your results here for the next 3.1 owner

https://www.thirdgen.org/forums/v6/1...dle-learn.html

 

Thanks for the info. I'll try it this week and post if any one suggestion helps.

 

I did the following two procedures back to back and they worked.

FIRST:
Cleaned throttle body with B-12 throttle body cleaner. Carbon melted off the throttle body. That stuff really works much better than CRC and the other brands I've used over the years. Put everything back together and connected IAC and TPS.

PROCEDURE 1:
Disconnected battery for 15mins to drain any residual power and reset ECM codes. Reconnected battery. Turn on ignition but DO NOT start engine. After 1min disconnect IAC plug from throttle body. Turn off ignition with IAC still disconnected at throttle body. Once ignition is off, reconnect IAC plug. DO NOT touch steering wheel or throttle at any point throughout the procedure. If you do, you have to start over from disconnected battery.

PROCEDURE 2:
Disconnect battery, wait one minute, and reconnect.

Turn off A/C.
Turn off Backlight Heater (rear window defroster).

Do Not Touch The Throttle at Any Point.
Do Not Touch The Steering Wheel at Any Point.

Set parking brake and chuck tires.

Start engine, let settle a bit (about 3-5mins) and put trans in drive (while parking brake on and tires chucked).

Let engine run until fan cycles on then off TWO times. This will take about 20-25mins to accomplish.

Turn off engine.

Wait five minutes.

Start engine and place in gear just like before.

Let idle for five minutes.

Shut off engine.

End of procedure.

The following is very important to remember......
If the throttle is touched at anytime during this you have to start from the 'disconnect battery' again.

If the steering wheel has pressure applied you have to start from the 'disconnect battery' again.

If the engine stalls at any point just restart and placeback into gear.