You'll want to search the list for "throttle rise". I've had this happen over and over, and it seems to be something that doesn't have a permanent fix, nor a definite cause. Things to look at are the IAC Valve and Throttle Body. Some people recommend having the Throttle Body cleaned. In any event, your symptoms sound typical - lift off the gas in neutral and watch the revs rise up 1-1500 rpms from where you were shifting at. Revs hang there forever, and the car won't settle into a normal idle (1200 rpm vs 750 rpm). Good luck.
