I hav a 97 camaro rs with the 3.8 and a 5 speed tranny. I've had problems with the car revving to approx 3000 rpm after I shift into neutral and when shifting between gears. It revs between gears but when in gear it returns to normal. I was thinking it was the throttle position sensor but I've also been told to think about the mass air flow sensor. No codes are shown when scanned. Any ideas would be greatly appreciated

 

A engine needs air to rev, A bad TPS or a bad Maf sensor can add fuel and take away fuel but they can not add air. With no vacuum leaks a IAC should not be able to get your car over 2000 RPMs. Most likely you have a vacuum or a mechaincal problem not allowing you throttle body to close.