97 Grand Voyager, runs fine with AC off, normal idle of 800rpm, but once AC is on, van idles at 1300rpm. Idles high at all speeds, when put in park will shoot up to 2200rpm, and when I turn the van off, it shudders. If I turn the AC off while driving, I still have the same problems. Thoughts?

When you turn on the A/C, the Powertrain Control Module (PCM) commands the Idle Air Control (IAC) valve/motor to open. This increases engine idle rpm to prevent engine stalling due to the increased load created by the A/C compressor. I'm guessing the IAC is valve is opening too far or is binding. It's located on the throttle body. Might try cleaning it and it's port in the throttle body. Inspect the wire harness and connections for anything amiss. Worse case would be a bad PCM ($300/400 + labor). http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528003c4be

Thanks so much RIP. I will have my husband check it out :)