Help! unstable idle

[mjmich]

Could an alternator that is on its way out cause my 96 cutlass to have a idle that is not constant,- it seems to flutter when upon shifting into reverse or drive. Sometimes it stalls. I get a SES light but dont have a scan tool. I just replaced plugs (delco platinums and magnecore 8mm wires). The car runs awesome except for this stupid idle problem.

 

-There has been a slight wine comming from the engine compartment lately.

 

Feedback appreciated

[Robby1870]

does your speedo and guages jump around? Like when braking to a stop, does the speedo needle go down smoothly, or jerky?

[mjmich]

Nope, Speedometer and rpms are fine; they don't jump around or anything. No warning light either. I just cannot figure out why this idle is the way it is- it is extremely frustrating. I can be trying to back into a parking space, and all of a sudden when i put my car into reverse, it just flutters and stalls. It's been like this since the GM guy changes my timing belt and i've tried numerous methods of idle relearn procedures.

[Robby1870]

Have you cleaned the IAC valve or had a new one put in? That sounds like another possible cause

[tgpguy21]

it could be like an o2 sensor. usually when the altenator is ready to go out you can hear lots of wierd noises. also when you step on the brakes headlights dim along with dash lights.

[conley3.1]

Most likely the o2 sensor. My car had the same problem, but i replaced the 02 sensor yesterday, and the idle+throttle response was approximately 1 billion times better. 8) But now the damn POS car won't start!!!

[SmokesGTP]

My alternator made no noises whatsoever. One day the charging light came on and a day later the car would have been dead had I not gotten the alt. replaced.

[mjmich]

Are O2 sensor and IAC very expensive?

[Slade901]

TPS is the mostly overlooked when diagnosing some Idle problems. TPS does fail and when it does fail, it's signal would confuse the computer. The computer rely on the TPS to verify the throttle plate's position when it is opening and closing.

 

TPS is cheap though.

[GP1138]

I've had idle problems lately, but that's mostly because I've been screwing around with my engine a lot. Mostly experimenting with different things, this week it's been the IAC, I've got 3 of them, one of them off my car, one from a 3.1 plenum I've had sitting around, and one from a j/y car.

 

Let me ask this, is the IAC supposed to have a huge effect on engine idle? I talked to a guy at Advance, and we were looking at my engine run, and he told me to unplug the IAC, and when I did he said it was supposed to run shitty. I think this guy is either full of it, or didn't know what he was talking about, but it didn't. I'm getting readings with my voltimeter from the IAC plug, and the car isn't stalling as bad, sometimes, tho, when I am coming to a stop, the car will bounce in idle. It'll go down to like 500, then bounce quickly up to 1500, then go back down and back up and so on.

 

I don't care much as long as I can drive it and gas mileage doesn't suck my ass. Gas is $1.63 this week for some Godawful reason.

[GPRACER]

Coolant temp sensor could also cause idle issues, the pcm uses this sensor to determine air/fuel mixture, check for corrosion in the plug, a pretty cheap and easy place to start or at least rule out.