gpagaduan

This is what I've been getting ever since the ZZ4 was installed three months ago in my 90 coupe. It wasn't that bad at first but now it's getting worse. I checked the archives and the archives say possibly to due:

1) bad MAF
2) bad plug wires, or wires not seated correctly
3) bad EGR valve, or not enough vaccuum
4) TB needs to be cleaned out

I don't think it's bad plugs or plug wire because my MPG is normal.
I don't think it's the TB because I would assume that my reputable Vette shop wouldn't put a dirty TB on my new new ZZ4 engine.
My EGR valve is new. It was replaced about month before the new engine was installed. I don't even know if EGR causes these symptoms.

I have a MAP sensor on my 90, correct...not a MAF?

Oh, by the way, this is what is wrong with my car. After the car has been driven for a while, it will stall when coming to a stop or after I've stopped. It won't stall as long as I'm giving it throttle. If it doesn't stall, it will shake like it's about to stall and then recover on it's own.

Any ideas? :confused: :mad

ittlfly

Sounds like the IAC may not be functioning correctly.

ROME

I had the exact same problem until this past weekend. I bought a throttlebody gasket kit from AutoZone and pulled the TB for cleaning. Check the tech tips section of this website for the step by step process.

I cleaned the TB as best I could, disassembled the IAC valve and cleaned it real well with a toothbrush, making sure to scrape off the very slight carbon buildup around the circumference of the IAC pintle. Didn't really seem like I did much at all, and I figured that what I DID do wouldn't make much of a difference. Low and behold, no more stumbling! The car used to die immediately if I tried to turn on the A/C at idle. If I was behind a car at a red light and had to give it any gas at al to pull up a car length, the car would die as soon as the rpm's tried to settle back to idle. No more.

I still have a little fluctuation right after coming off the gas, but now the idle will usually linger on the high side for a couple of seconds and slowly settle back down to about 600-700 rpm. This last little bit of tuning that is needed is definately the O2 sensor (car is running consistantly rich). I'll replace that this weekend and all should be perfect. I'll post a follow-up after I replace it.

Good luck,

Rome

oldace84

Probably not really important...what about the fuel pressure.....plug gaps....Hei ditributor...cap and etc.......have you already checked this...if so sorry...just a thought.....what about the fuel filter?????

Try anything....trying to help.......but............

tony


:nopity

gpagaduan

Ittlfly, you hit the nail right on the head!!! I went to the service manual and it says to reset the IAC valve everytime it's disconnected. I can't believe the nationally renowned vette shop that put in my new engine did not do this, nor did he diagnosis this after I brought it back. He suggested that the aftermarket fuel injectors were the problem!!! (Actually, the mechanic is awesome and except for the IAC problem, my car is almost perfect with my new ZZ4) Keep waving at the C5's...it confuses the heck out of them :) :yesnod:

ittlfly

Glad it worked out and didn't cost you any more $.