I've got a 94 Automatic LT1 that's been having this problem for quite a while now. When the engine's hot (halfway) and in gear (at lights) the engine revs up and this leads to the car jumping forward. Taking the trans out of gear (N or P) makes it stop.
I've replaced the O2 Sensors, I've replaced the IAC valve and EGR valve hoping that it'll solve the problem. Actually, it worked fine for a couple of weeks after the EGR was put in but returned last week.
Also, I seem to smell Gasoline everytime I get off the car after driving for a while. Any ideas?
Any input will be greatly appreciated.

 

Mine did the same thing a while back, turned out my intake elbow was torn and sometime unmetered air would get in and the ECM would try to compensate, which would cuz the RPM's to jump.

 

Thanks for the advise. I will check into the intake and see if there's any leaks. Just a question though ... could this be a problem with the MAF? It does it only when hot (over halfway) and not when cold.