RPM idle drops then returns
 

'02 with 85,000 miles has had MAF changed months ago. Just started to notice when running without A/C, idle takes a little drop from normal speed and then goes back up (of course I believe it's the same with A/C on).

If there is anything simple I can check before I head to the shop, I'd love to know. Tom

I recently had the same symptoms. The car would even stall with the a/c on. I replaced the idle control valve. It's an easy diy job. I think i paid between $180 and $200 for the part. After installing the new part, I was bummed out when first test driving the car because the idle still wasn't normal. I figured I'd misdiagnosed the problem and just pissed away $200. The good news is that after putting fifty or so miles on the car, the idle settled to its normal rock steady idle of 700 rpm. I've heard that the ecu needs to adjust to the new part. And sure enough, it was true. After a few drive cycles....perfect!

02 with 85,000 miles > if you haven't service/clean the throttle body assembly then you might want to start there. After I've cleaned mine it really made a world difference in RPM stability and responsiveness. The gunk I took out of that thing lollll Was quite embarrassing in fact

Possibly unrelated I understand but this is where I'd start with that sort of mileage and RPM issues (if you haven't done it). Few DIY articles around on the Pelican Parts website I'm sure, procedure takes about 2~3hrs max. doesn't hurt!

Carb Cleaner aerosols/can/sprays; wear a mask and glove if you use ;)

It could be a vacuum leak too. Mine was dropping idle and would almost die if the ac wasn't on. I found I had a cracked oil fill tube when I removed the engine cover and started poking around. There are many places on these cars that can happen. I usually find them by just listening for sound changes when i poke and prod on areas that have a vacuum on them.

Absolutely, start with cleaning the throttle body. I threw hundreds of $$ at my 2000 Boxster. Cleaning the TB was all it needed. It's a very easy DIY.