[shorod]

Since the idle doesn't drop with the A/C off that would suggest the either the compressor is close to seizing up or the Idle Air Control (IAC) servo is not effectively doing its job. You could further test the IAC by turning off the A/C with the engine idling and stopped, then turn the steering wheel all the way to one of the locks and hold it there for only a couple of seconds. If the idle speed drops like it does with the A/C, that further points to the IAC. Don't hold the steering at lock for more than a few seconds though as it is reportedly hard on the pump.

-Rod