Rough Idle

When I rev up the engine and then let off the gas, it goes below idle for a split second and then comes back up, and when the engines hot, the idle will randomly drop very low and then recover a few times, then its ok for a while. Does anyone know what could be causing this?
Thanks, Ben

does it only happen when the a/c is on, or a/c fan?

im looking into buying this immaculate 1986 944 and it has the same problem. No noises, the car just runs rough, bogs down, but doesnt die. in this case, the a/c or the fan was NOT on.

mine does it too, but only when i rev then let off the gas... come to think of it, it does do it while idling. but the rpm difference between idle and the bog are like 50-100.

There is a ISV down there by the intake. It is known to go bad on occastion.
There is also the shutter problem in early 944 cars. You can read all about that at www.frwilk.com .