I would not go out and replace a TPS unless you know for sure it is faulty. There are a couple things that influence your engines return to idle. One is the throttle follower, which is programming in the PCM that steps the Idle Air Control (IAC) motor to bring the engine gracefully back to idle. The other is the IAC itself, which may just require cleaning. I can verify some things this evening if I have time by plugging the old laptop in and check the voltage feedback to PCM from the sensors to see what the TPS is registering after you immediately let off the throttle.
How it all works...
Unlike a carburetor, which always has the throttle blade partially cracked to allow idle air by, a throttle body closes tight not letting any air by. There is a small air bypass circuit that is regulated by the PCM through the IAC motor. When you let off of the throttle to 0% open, then throttle follower programming steps the IAC motor at intervals allowing a smooth part throttle to no throttle air transition. If you did not have a throttle follower, the engine would just stall when you left off the throttle. If there is no malfunction with the TPS, then I would check to make sure your IAC motor is not fouled resulting in a slow return to idle response. If both are in good shape, then it is the programming used to regulate the throttle follower.
-Muzzy
