Weird idling with A/C on

[Nygdup]

89' 325i Automatic.

Recently recharged the A/C and started running it for the first time since I bought the car. I've noticed that when I run the A/C the car idles (or revs) very inconsistantly. I'll put the car in park, and the engine may idle at just under 1000rpms, or it may shoot up to over 3000rpms.

It'll rev up, kick down, then rev back up again. I can even feel the uneven revs when the car is in gear, but it's not as obvious because the drivetrain keeps the car from overrevving. What could be causing this?

[jlevie]

Stick ICV or faulty Idle Control Module. Intake leaks or a bad AFM can also be contributors.

[wagonizzle]

Mine did goofy shit because the TPS was out of spec

[Nygdup]

OK... I'll look into those. Seems weird that it only acts up when A/C is on.

Thanks for the help.

[Dibo718]

Sounds like a stuck idle control valve, my brother is having the same exact issue in his e46 and has replaced everything but the ICV, im willing to bet that is your problem.

[AlarmedBread]

FWIW - my car idles a little funny with the AC on too. Only a tad higher and fluctuates between 800-900rpm. I've taken everything apart and cleaned and all sensors, wiring, relays and computers are good.

Good old primitive fuel injection. ;)

[Adrian_Visser]

of course you guys do know that the idle is supposed to bump up with the a/c on to compensate or the extra engine load

[Nygdup]

bump up, yes... go to 2-3000 + rpms, no.

Haven't had a chance to replace the ICV yet. Car decided to have cooling issues before I could address this.

[Restoman]

Did the compressor spin freely? It might be bad compressor.

BTW I love this icon :hitler:

[Nygdup]

Did the compressor spin freely? It might be bad compressor.

BTW I love this icon :hitler:

Dunno.. never thought to take the belt off and see. I'm a total newb at A/C systems.

[HST]

you can try to clean out the ICV with carb cleaner. When you take it out ther is a metal "flappy thing" that should move back and forth freely, most of the time there is gritty black stuff in there. If it helps some but does not fix it, you may need to replace it. It is cheaper to clean it out first to make sure that it is the issue.

[Alan_525i]

I'm experiencing this same exact problem.

We tried a new ICV, no change. Car idles at 800-850 with AC off. Same large range of potential idles as the original poster.

Anyone else have other ideas? I'll check the TPS and AFM, but they should both be good.