1989 Chevy Cavalier rough running

The idle air control "IAC" is supposed to compensate for the added load of the AC compressor on the engine. If this vlave is carboned up or not functioning it will cause the problem you described. Hope this helps.

Hello - This could be several things, MAP sensor that you need a scan tool to check, your IAC that you need a scan tool to check or, you could do the check below. To check the IAC motor remove the unit, with the wires connected turn the key to the "on" position without starting the engine, the IAC should move in or out. If the IAC motor does nothing it has probably failed, replace it with a new unit and recheck system. note: while the IAC motor is removed clean (use aerosol carburetor cleaner) the passages the IAC uses to control idle air speed. We need to check a couple of things to possible help in the diagnosis. First, please go to Auto Zone or O'Reilly's and for FREE they can pull the codes to the car. Most important: Once they check your codes, if they find something and you don't get it fixed and need to get back with us, please make sure you tell us exactly what the code was, number and all. Example, if the code was E0568 O2 Sensor bad. Then make sure you give us all of that. While there for FREE also they can bring their tester out and check your battery, alternator and starter. Also, it could be a vacuum leak. With the engine running please do two things. One, take a spray bottle of water and mist all over the plug wires and see what happens. Next, take a can of carb cleaner and spray around the intake manifold where it mates to the engine and see if the engine revs slightly. When was the last time you did a tune up, plugs, wires, filters etc? I would also like for you get a fuel pressure check if possible. Please do the above and get back with me on the results. Please let me know the exact vehicle model, I have attached the choices. Last, you may have a couple of safety recalls that may apply to your vehicle that the dealer would repair. Please contact the service department and provide your VIN number and have them check to see if it is your vehicle.