3.1 v6, New TPS, new IAC, new CTS, I never noticed if it happened before I replaced those things, but when my car is in neutral, it will idle up. In drive or park, my car idles at a steady 900-1k rpm's, but once I drop it in neutral it will idle up to 1500 within 10 or 15 seconds, and just keep going up, until I give it some gas, and then it drops back down to 1k-1100, but starts idling up again.

Any ideas? Doesn't seem to be a huge deal, but, as everyone knows, especially on a car, something small ignored turns into something huge.

 

How long has it been since you replaced the parts? You may need to disconnect the battery for 10 seconds and drive the car for a half hour afterwards in stop and go traffic to do an idle relearn since you have a new IAC.

 

I replaced them awhile ago, but I also replaced the alternator recently, so the computer would have reset when I did that.