I have a 325 is 1987. when the a/c is on and the car warms up the revs go up to 21-2500, it remain there for a while and then it drops down to 900, and it goes back to the same cycle. It only happens when the a/c is on.

Changed the idle valve. Still same problem. Help!!!!!!!!!!!!!!!!!!! what else could it be short of experimenting $$$$$ with something else

OK, you do know Sam?

He is the KING of idle.

http://www.mesaperformance.com/faqs/idle.html

But as a real deal shortcut, consider adding a restrictor whith a 1/4 inch hole up stream of the idle air valve, thus restricting the max air it will flow.

I use a rubber washer to restrict mine.

Later,

I have had this happen a couple of times on my 88 325i it seems to come and go by it self (AC or no AC) Wierd, The IAC makes a ton of flucuation but the Haynes test checks out ok.

Also have any pics of the fix?