Idle drops with Air Cond running

[SpikeJr]

New to the Boxster. Have a 98 2.5L and she runs a steady 800 rpm (about 780 if I really look close) without air conditioning selected. As soon as I turn on the AC, the compressor kicks in and that causes a drop in the idle rpm to 500-600 rpm. Then it will rev up to close to 1,000 rpm before settling back to the 800 rpm range. Sometimes I can see a drop as low as 400 rpm. Never stalls. However, when I'm going slow (ie: parking lot) and I have to be on / off the gas, each time I come off the gas with the clutch depressed it sure looks like it's headed for a stall. Is this "normal"? If not, any thoughts on some areas I should focus on for troubleshooting? Since I just got the car, I thought I'd start with a fuel filter as a possible weak area...