PCM is for Powertrain Control Module. It's basically the computer that monitors your engine and controls all the ignition, ATX shift points and other stuff.
The MAF (Mass Air Flow) just measures enses how much air is entering the engine through the intake for the PCM. You could probably get a stock MAF at a junk yard for $50. (No reprogramming or flashing needed!) Before buying a new one, you might want to clean the little sensor wires in the tube with a spray of electonic parts cleaner. (Radio Shack)
