[A8ked]

The idle control valve is indeed expensive, the Porsche part # is 996-606-160-01, there is also a Bosch part # 0280140572. There is a gasket #996-110-310-50 between the idle control valve and the Throttle body that you will need to replace.

The idle control valve can easily be removed and cleaned which you may want to try before you order a replacement. It's attached to the left side of the Throttle body there are two electrical plugs on it and it's held on with two screws. I'd suggest you remove it and give it a good cleaning with Carburetor cleaner.

You don't say what year your car is and what engine you have, the information I've given is for a 2.5 engine from 97 to 2000.

You may want to check prices with Pelican Parts or Design 911. There are several for sale on USA EBay for $50 to $100. used. If you look at the Pelican Parts web site they have some information on the valve. If you search this web site there are several items related to the idle control valve. You may also want to google the part number there are lots of details related to the valve.

Here in the USA most people seem to favor Durametric.

I found that cleaning my idle control valve solved my rough idle issues and it only cost me a couple bucks for the gasket and some carb cleaner!