1989 firebird trans am. TPI this car is driving me crazy. I Don't know how many idle control valves that I replaced and followed a number of different ways to set it up from youtube. It stars great. No check engine light. Then the idle drops below 900, check engine light starts flickering then it idles up check engine light dissappears then it idles down check engine light comes on flickering then solid lit then the engine repeats itself until it does its last idle down and stalls. I've been trying to fix this for about a year. Does anyone know the proper way to set up a new ICA. I got so many things to do on this car and time is flying by me. There has got to be someone who had this issue and knows how to fix it.

 

Doesn’t sound like a bad iac, does it act up when you tap on the ecm case while the engine is running?

 

Considering it's supposed to idle at around 600 or 650, ...

I'm guessing those "numbers" you're giving us are hallucinations or fever dreams delivered by the "sport" wavy-pointer trim package in the dash? The one that's notoriously inaccurate, specifically, always failing by reading WWWWWWWWWAAAAAAAAAAYYYYYYYYYYYY higher than reality? Kinda like one of the ones I have, that reads right at 3 times the actual RPMs?

I'd suggest you ignore that dash-mounted POS entirely, and set the idle parameters properly, using a piece of actual test eqpt of some sort for your RPM readings. Which is, fully close the IAC valve (sorry, I forget which pins you put 12V on to run it all the way that direction), leave it disconnected, run the throttle stop in a couple of turns past where it starts to open the throttles, start the car, gently let the throttle off if you had to push it, and set the throttle stop to idle at 400 - 450 according to something accurate; then shut it off and hook the IAC wires back up. This allows the IAC to close most of the way during normal idle, butt leave plenty of room for it to bump it up when the AC comes on, the alt sees a heavy load, or whatever else.

 

Never tried that. I'll try it. I forgot one thing. The idle drops when the electric fans turn on and the check engine light appears.
thanks

 

Are the fans kicking on at a higher temperature like 228f or does this happen at a lower temperature?

 

Low temperature only.

 

Sounds like a bad ecm or possibly a cts reading issue. Fan gets commanded with a/c request as well as cts reading. If it’s coming on sooner I’d suspect the 1227165 ecm is bad .

 

Thank you.

 

Of course the idle drops. The fans put a significantly higher load on the alt; it can't miracle up electricity out of nothing, gotta get power from somewhere; gotta be the engine. OF COURSE the idle is gonna drop, especially if it isn't set right, and the IAC motor can't bring it back up.

Probably not a "bad ECM". While that happens of course, it's quite rare. Wouldn't be the first "go to" "explanation" in a situation like this. Might eventually get there, of course; just, not the first conclusion to immediately jump to.

The CEL is a SYMPTOM of your idle settings being messed up. Fix the idle as described, it'll potentially take care of itself.

 

Have you checked for stored codes?
any mods to the car ?

 

I understand that the idle will drop when fans turn on. However, so much that the engine will stall. I don't want to mess with that idle screw. At least for now until all other potential problems are ruled out. I'll check for codes. I should have done that many months ago but I got involved with other issues on the car, which are a few. The car is stock with no mods. I should have used the car instead of having it sit. Thanks.

 

Nothing wrong with giving the screw a little tweak to nudge the throttle plates open a touch just to test it.

 

Do we know what PROM is installed in the ECM? Some of the aftermarket tunes and some home-brew tunes might not have the stall saver parameters active or steep enough (IAC adder/attack rates). Even the factory parameters could be light with double high-watt fans loading down the alternator.

Just in case you expose the ECM for the tap test, it could be educational to pull the window cover screws and look at the CALPAK for a version.