in desperate need of a fix

[intern8tion9l]

ok, so i haven't driven my car since last july because of this awful problem i can't solve, and i really would like to this year. i just purchased an ecm, but am told it won't likely help. i'll do my best to explain what's going on, and maybe someone has some intel....

when i start the car, it idles up a bit, then back down to around 800-900 rpms, like a normal car. however, as soon as the cooling fan comes on, it idles up to 2000-2500 rpm, and will not come down until i shut the car off. same thing happens if i tap the gas while it is at a normal idle. to add to the weirdness, if i unplug the iac when it is at a normal idle, rev it up a couple times, then plug the iac back in....the car will run pretty normal until i shut it off again.

i have replaced the iac, coolant temp sensor, and tps. the upper and lower manifold gaskets were changed a few thousand miles ago, and i have checked them and all the vacuum lines for leaks. seems electrical...any help you guys can provide would be awesome. thanks!

[Prospeeder]

actually it does sound like it  could be related to the ECM, if none of the sensors or thier wiering are bad, then theres only one thing left...

[flybynite]

Sounds like the ECM. The chips do go bad but not very often...

[pontiac6ksteawd]

My TGP also does that. I went thru about 5 idle relearns, and it finally quit doing it, until I put the car in storage, and unplugged the battery. Then had to do it all over again.

[intern8tion9l]

mines 5spd though, so no idle relearn

[pontiac6ksteawd]

I personally dont think it matters if its a 5 speed or not.. The computer has to learn how the engine idles thru cooling fans, and whatever else, taking a draw on the system, and the system responding to that draw.. but thats my opinion..

[intern8tion9l]

swapped the ecm today. no help

[TGPilot]

Sonds to me like the IAC stepper motor is getting lost in the number of steps it is running in and out. Like it is not finding it's home position until you force it to recycle in and out...plugging and unplugging while running. Get a jusk yard IAC and give it a try. If it works, go buy a new GM one so it lasts longer than two weeks in the car. ;)

[intern8tion9l]

i have already tried a junkyard iac and a new out of the box iac. neither helped. this problem is beyond me, but i'm taking any steps and suggestions

[TGed]

Check your grounds.  The main ground for the o2, map, and ecu should be on the back stud bolt for the trans housing.

[GPChief]

Check your grounds. 

x2

[intern8tion9l]

took out the burned chip and ran the stocker.....car runs at an even higher rpm now and throws code 22(tps low voltage) and code 23(mat low temperature)