Hello all,
I have a 1989 Firebird, 305, TBI, VIN Code E, with Calif emissions. I have a question about the idle, I've been haveing problems with the idle rpm. Its seems to be erratic. I can be driving down the road and let off the gas and still have high idle, I put the car in neutral and I have 1500 rpm. Next I replaced the IAC valve and adjusted it with no luck. So I put the ECM in diag. mode which extened the IAC and disconnted the connection, takeing the IAC out of the TBI. I am still haveing problems, its weird, when driving the RPM is ok, when I left off the gas it still has high rpm then I step on the acceraltor and then the idle goes to normal. Its like haveing an a spring choke. I have no idea whats going on here, I have no error codes, and the car runs like a champ. All and any information will be greatly appreciated.

Brad
San Deigo

 

that is interesting... Does it both in gear and out of gear? What does the throttle position sensor read at 0% throttle? WAG but maybe its worn and sending erratic signals when the throttle is closed.

 

What should the TPS sensor read at 0% throttle?


R

 

Mine is doing the same thing. I've checked almost everything I could think of. It's been doing this for quite some time now, I've just never posted anything about it cause most people here aren't really interested in helping, they just want to call you stupid and blow you off. Oh well, the engine swap is coming next spring so I dont have to worry about it too much

 

Sounds like a vacuum leak to me... check all hoses and tubes. That's the typical cause of a high idle. The other is the throttle blades idle position is a little off allowing more air in than it should. A quick adjustment with a screwdriver can usually work some magic. I'd check the leak first though.

 

Does it only do this while your driving and not just idleing at a light? I think the computer uses teh iac to keep the rpms slightly elevated while the car is moving and in gear to reduce any jerkyness when you let off the gas while in gear. I dont know this from fact but just by observation the computers in my gms seem to do this. Makes downshifting in my s-10 useless because the iac is open while im moving.

 

Update:
Check all vacumm lines and linkage..everything is good. Throttle blades are in correcte position. I replaced the IACV and the TPS. The car runs great, I have had two idle problmes, only when the AC is turned on. First while driving I let off gas and put car in neutral the rpm was steady at 1600, turned off AC and went back to normal RPM in a matter of seconds. 2nd while driving, the ilde was bounceing around from 500 to 800, very weird, turned off the AC and the idle went to normal. What would cause this, is there a sensor for the AC?? Any comments or suggestions, besides keeping the AC off, time to go to work, thanks for all the help. What is WAG?

Brad

 

a/c cycling/wasted compressor will cause the rpms to bounce around. The dumbass that owned my car before me never put any lubricant in when he recharged the a/c system and talk about a funny idle. It almost stalled whn i turned it on. Smoked the compressor the first time i used the a/c.

 

well, whats funny about the whole ilde AC thing is I just replaced the whole AC system about one month ago, could have gotten a bad compressor. Where does the ECM get the singals from the ac to increase and decrease the rpms?? I think I have it narrowed down to the AC circuits

Brad

 

i think the ecm just does it by load. It sees the rpms drop and it opens the iac to compensate. When the compressor cycles off, the rpms rise up because of the sudden decrease in load. Listen and feel the compressor. Mine made lots of noise and vibrations and got REAL hot because of allt he friction.