What is PCM and what does it do on 1996 Chevy Cavalier z24?

The pcm (programable control unit) or ecm, hase the same function for all cars. It's a computer that basicly runs the engine (along with other things) in the car. It takes information from all those fancy sensors on the engine (o2,crank,tps..) to give the engine what it needs. It will adjust fuel flow, spark timing, idle speed, ect, all depending on outside temp, throttle angle, vehicle speed, ect. Why dose this question come up? Do you have a problem?