Chevy high idle - 2000 Chevrolet Venture

The number one cause for high idle is an imbalance in air pressure, An engine that is idling too high may be caused by a faulty idle air control motor valve that has completely failed or that has simply become weak and is not functioning correctly. God-Bless!

A temp sensor out of range giving a false cold reading can cause high idle . A MAP sensor can also cause high idle by advancing the timing resulting in higher idle .

High idle speed on a vehicle with fuel injection is usually caused by a faulty idle air control valve or a vac leak.

Interesting. If it is a vac leak you should be able to plug the line from the intake to kill the leak.
My guess would be the idle speed control is raising the base idle to cover the load the ac compressor would put on the engine.
If the compressor is not working, the computer would not know.

Peck on it with something to see if it idles down, if it does you probably need a new idle positioning sensor.

Check for a stuck open EGR valve,it will have to be removed to be checked.Or you have a large vacuum leak,either one will increase idle and fuel causing hot cat and high idle.

distributor is advanced

CHECK TO MAKE SURE THROTTLE LINKAGE IS NOT STICKING.ALSO LOOK AT THE THROTTLE BODY GASKET.IF ITS LEAKING OR BROKEN IT WILL CAUSE HIGH IDLE SPEED.IF ALL LOOKS GOOD.SCAN IT.CHECK FOR IDLE SPEED CONTROL FAULT.IF IDLE SPEED CONTROL GO BAD IT CAUSES HIGH IDLE SPEED.

i would first check for a vacuum leak because this is considered a newer vehicle and does not have an idle screw, so I would get some "brake kleen" and mist it at each vacuum hose, if the idle changes then change that hose it means there is a leak, and that should sove your problem, if it doesnt , I would then check /replace the idle air control valve as this is the motor that controls the idle

If your idle is going from 500rpms to 1000rpm's fluctuating at and idle your EGR valve is probably carbon up and needs cleaned or replace.