I have a 1988 GTA 5.7 L, with automatic that is driving me CRAZY!! When motor is cold, car starts and runs normally. As it begins to warm up the idle drops way down until the motor almost stalls. If you put the car and gear and raise the rpms it begins to miss and occasionally will backfire. If you drive the car from cold, as it warms up, the motor begins to 'surge"; almost stalling and then recovering. When it reaches operating temperature it is like someone turned off the key; it will instantly stall. I have checked the fuel pump; changed the plugs, wires, cap, rotor, and checked as many vacumn lines as I can. Even changed the ECM with one from a parts car that we have (an 1987 GTA with a 5.7 L) and still nothing. Everything seems to be working fine. Suggestions???

 

ignition module or pickup coil...

definitely electrical...and ignition...

 

Full state of tune? Any codes? What part of the country?

 

Thanks for the response. Ok; I live in Ontario, Canada, but the GTA came from Kentucky. Have done a complete tune up; plugs, wires, cap, rotor, air filter & fuel filter. Have changed the ECM. Tried last night changing the iginition coil & module. Still no change. Have tonnes of spark, but the plugs are black with carbon. Noticed last night that there is a huge amount of pressure in the gas tank when the car heats up. Replaced the plastic vent valve at the tank, nothing. Only way to keep the pressure from building is to leave the gas cap off.
HELP !!

 

That is surprising that it wasn't the ignition module or pickup...

You are running rich...as indicated by the blackish plugs. A couple of other possibilities...It is possible that you have some bad injectors. I have seen injectors where the solenoid will tend to not function as the injectors warm up...I would test the impedance of the injectors both cold and warm...verify that they are all within spec of each other.

Another possibility is the fuel pressure regulator going bad. The computer can only correct so far for a rich condition.

If you aren't getting any codes, it is likely more of a mechanical problem.

Also, for the tank pressure, maybe your gas cap is bad...try a different vented cap.

HTH...

 

Also, have you checked the Idle air control motor? Maybe it is having a problem as it warms up due to a weakened motor...

Do the adjustment on that...

https://www.thirdgen.org/newdesign/tech/tpimod2.shtml

 

Thanks! I will try these suggestions! Sorry about not mentioning codes; it was giving so many that we were looking for a common thread between them, rather then figuring it was each seperate one. It was giving off 22, 34,35, 42, 54 and a couple of others. The common thread seemed to be the ECM, which we swapped; ignition and/or fuel. The only other common idea is the EGR.. would that be possible?

 

For whatever reason, i sounds as if the motor is going lean. Check for airleaks around the MAF and vacuum leaks for starters. Could also be a failing fuel pump. W/o actually doing diagnostics, though, these are just guesses

As for teh codes, reset the computer and see which codes comes back up after you drive the car.

 

Thanks so much for all the suggestions!! Going to go and give them a try tonight... hope something works! I absolutely love firebirds, but this GTA is definately pushing the limits!
And did try changing the gas cap; but it didn't make a bit of difference; still a huge amount of pressure in the tank. Are there any vent tubes or lines other than the plastic one just outside the tank that could be plugged?
BTW this forum is the greatest thing! I have learned soo much from just reading all the other postings; and its great to have all this help. Thanks again

 

Hi again; ok.. well here's what we tried and here's what happened. Replaced the pick up coil, adjusted the idle air control and replaced the fuel pump relay. Once we adjusted the idle, the stalling stopped, but now the car starts and goes up to over 1500 rpms as the motor warms up the idle increases! We set the idle according to the directions here; set for 450 rpm and should get a 600 rpm idle in drive! Only code we are getting is code 34 which is the MAF sensor; or the MAF sensor relay??
HELP !!!