1999 Porsche 911 Carrera Idle hangs when rolling

I have a 99 3.4L 911 (996) with a 6-speed that is suffering from an intermittent idle problem. Sometimes when I clutch, usually at speeds over 35 mph, the engine rpm hangs around 2000. If it's cold outside it might even hang as high as 3500 rpm. Everytime I clutch, it will continue to hang until the speed of the car drops below 10 mph. Once it hits the 10 mph threshold, the idle will instantly drop to about 800 rpm, which is the normal idle speed.

I can't find any rhyme or reason to temperature of the car or weather conditions when this happens. It seems completely random. Somedays it will do it all day long. Somedays it will just do it one cycle, and then quit the first time I come to a stop, which caused the idle to return to normal.

This only happens when I'm rolling above 10 mph. I cannot get it to happen at a stop.

The car gives no codes on both an OBD-II scanner and a Durametric scanner.

So far I have tried changing the IACV, changing the TPS, changing the MAF, cleaning the throttle body, cleaning the temp sensor connection, checking the throttle assembly for binding, checking the accelerator pedal for binding and searching for vacuum leaks.

My mechanic was no help as the car wouldn't do it while he had it, so that was a waste of $100. This is driving me crazy. Do you guys have any ideas?