Why does a 1993 Plymouth Colt 4 cylinder engine idle rough when the air conditioner is on?

Hey Bill== An a/c takes about 20 horseower to turn the compressor and a 4 cylinder is developing about 30 horsepower idleing so it will slow down and be rough. Sometimes there is a solonoid to help compensate for this but it doesn't help a lot. GoodluckJoe Check your idle air control valve for lack of movement. When you turn on your A/C it puts a load on your engine, the IAC valve compensates for this by increasing the idle. If it's bad or is not being controlled correctly that rough idle you described will occure due to the load on the engine. Regards, Kevin