How do you diagnose fast idle that slows to 1200 RPM?

Start with looking for a vacuum leak.

I have checked for vacuum leaks and found none. I have a strong vacuum at all RPM ranges. I did remove the cover on the side of the Throttle Body and I can see the electric motor keeping the butter fly open longer than necessary after revving the engine. I also can disconnect the plug on the Throttle Body, turn the gears to an idle speed of 900 and the car runs great. I can also so say the car has more power with the Throttle Body disconnected. It seems the computer is telling the Throttle Body to keep the butter fly open.