whats wrong with my truck?

i have a 1995 chevy silverado 1500 ext. cab truck with a 350 and a throttle body and around 242xxx mile on stock engine and rebuilt transmission but my problem is is when im stopped at a stop light or leaving it in park while running the rpms of the engine cut of and it seems like its wanting to still run but then it jus cuts out completely but before it does it sounds like rushing air going into the throttle body ive replaced the map sensor , egf valve, fuel filter, fuel pump and nothing seemed has to work any idea what it might be im thinking a sensor might have went bad but i have no clue what 1 it jus seems as though it sucks to much air into the throttle body and then it dies and makes the whole truck shake