Whats wrong with the Ford Ranger?

I have a 1991 Ford Ranger 2.3 with a 5 speed and every now and then, usually just when the engine is cold, it shakes like crazy and barely stays running at idle (Sounds like it is missing almost). The "PIP" senor and EGR was just recently replaced. Let alone it has no power when it is doing the shaking thing and revs up real slow and barely drives. After the engine warms it kicks in with full power and drives like new. Thanks.