My Dad has a 89 2.8 V-6 firebird and this is a strange problem. Can anyone help? First if I start it it will be fine but after it runs for a while in the garage or in traffic and really warms up (like about 220) the engine will start to fluctuate in RPM's from idle to about 400 RPMs to 1700 and eventaually stall. Any time you restart it it will either stall or do the same thing again. If you rev it as your starting it will hold a steady RPM untill you let off the gas, but even if you rev it up and put it in gear the engine will die. I have checked for computer codes and get none except for the normal code 12. I also put it in field service mode and it operated alright (open loop until the O2 sensor warmed up then closed loop after that and wasn't running lean or rich) This car has gone through 3 or 4 O2 sensors in a short time. The other strange thing is I started disconnecting different sensors to see if it would change the engine problem like the MAF and Throttle position sensor but afterwards still no codes showed up in the ECM when the should have!! Is this a problem with the ECM? I also checked all fuses even underhood fuses and they all were ok. One other thing I stuck a screw driver in the underside of the EGR valve and reved the engine and it didnt seem like the valve was moveing like it should. Actually it didnt seem to move at all. Can anyone help should I change out the computer? It was brought to a garage and they couldn't find anything wrong with it either!

 

Sounds like it needs the IAC cleaned and adjusted...

 

ok i have the iac valve in hand it is pretty dirty so i am about to clean it but what do you adjust it to? the chiltons says not t adjust an old one but when installing a new to just make sure it is below 1.102 in (28MM)

 

ok I cleaned it and make sure it was below 28mm I think it was about 25mm (in or around there) I reinstalled it and started it it up but no change. Is there a specific setting for the IAC valve or does anyone else know what might be wrong? I still think it might be the computer but I dont want to spend the money to start changing part if Im not sure thanks.... Erik

 

Ok i found the articale on how to adjust the IAC valve. Well as i tried to do it Paper clip to a+b termanals of diagonstics port and IAC connector disconnected and tried to start it up again it was still doing the same thing -RPMs fluxing and then stalling so I dont think its the IAC. Can anyone give me an edjucated guess in the right direction?

 

oh yeah also if it helps as the engine is about to stall the check engine light comes on but as the engine recovers it goes off and then repeats the cycle until it eventually stalls but still no codes saved!! I'm stumped on this one??????

 

Does anyone know what this might be?