Intermittent Idle Problem, A/c Related Options

[Poonicus]

Alright so since about 3-6 months ago I've had a rough idle problem whenever the a/c is on, but whenever the a/c is off the car is perfect and this is Texas I kind of need my a/c on. Whenever the car is at running temp and even cold it idles fine at 800rpm but whenever you turn the a/c on it will go up to 1100 or so and then it will shoot down to 100-200rpm and the whole car shakes. I was wondering if this was because of incorrect belt tension, a vacuum leak, bad iac, or because that's what the celica's do when the a/c is running. Any help would be appreciated.

[VavAlephVav]

First I would watch the ac compressor while its running, does it "rattle" at all. It may be that there's extra friction in the compressor because it needs a little more oil added to it.
The ac compressor oil is in little cans at O'Reilly you can add it through the low side port with one of the small hose fittings they sell. If the compressor is noisy you just add a little more
Oil to it until it shuts up, probably less than 4oz.

Otherwise I would guest maybe there's a vacuum leak somewhere or the IAC is not working properly. But if it idles normally without the ac then the vacuum leak might be more likely, or something in the vacuum system.

[Box]

A/C idle up valve could be at fault, it'd be the first thing I'd check anyway.

[VavAlephVav]

Ya I was looking for more info on that but the Toyota manual I have on the 5sfe/3sge does not call it that same name. What do you think they call it? This book was old and then made into a PDF in 2002 so the bookmarks don't always work right, I can't even find the system the vacuum system should be in.

[Special_Edy]

AC Idle Up Control Valve according to the vacuum routing diagram under the hood. It is located on a bracket bolted to the passengerside of the intake manifold. The ST uses an interchangeable unit, but it will not properly mount to the bracket. The only source for them is the salvage yard and possibly a dealership, auto parts suppliers dont carry them.

The fact that the idle initially increases leads me to believe the IUCV is functioning correctly. Try unplugging the electrical pigtail for the AC compressor/compressor clutch located on top of the compressor and under the alternator. I THINK this should cause the idle to increase regardless, and prevent the compressor clutch from engaging, though the system may be smart enough to do neither if it senses the compressor not building pressure. If the idle does increase and the car doesnt begin idling rough, this would mean the compressor was the culprit.

[Poonicus]

I don't think that it would be the idle control valve but anything could be possible in my opinion with the car it vary well be that is has a vacuum leak. I think I might just redoing all the vacuum lines first because I've been wanting to that anyway to clean up the engine bay anyway. And thanks for all the help guys, sorry it took me so long to reply been busy with work...