Idle drops with Air Cond running
 

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...

Mine is a '99 2.5 and the rpm drops maybe 50 at the most when ac is turned on. Something doesn't seem right. Fuel filter would be a good start. Wouldn't hurt to clean the maf as well, though your normal idle seems right on. I would have the ac checked.

The ECU is programmed to compensate for the load of the a/c compressor at idle by increasing the air/fuel flow so the idle remains relatively constant. It sounds like that function is not working properly. I'd look at the MAF or the idle control valve.

A partially clogged fuel filter would typically work ok at idle (very low fuel flow rate) but not flow enough fuel at high speeds and you'd get lethargic acceleration and poor performance at high throttle openings.

Appreciate the response! I'll look into the MAF for sure and let you know....

Did you end up determining what it was?