"Never gun the throttle lingage on the carburator when adjusting the idle speed because the manual for your 75 Chevelle says to adjust it in drive. The car will jump the 4x4 chunk of wood you used for a wheel chock with no problem. And if you happen to live across the street from a bluff you could come very close to exploring the woods below if your not hanging on to the steering wheel with your legs hanging out the door while your trying to shift the transmission back into park(it will just keep going).