When I turn AC on engine surges up and down. Why and what is wrong. Have changed all belts, and replaced tensioner for AC.
First thing to look for is remove the intake boot at the throttle body, and look at the throttle plate area. If there is black carbon around the throttle plate where it seats, clean it with carburetor cleaner. Put it back together and start the engine. It will be flooded so hold the throttle open until it starts and clears. The idle should start out being high so let it run at idle for a minute to let it stabilize. Turn on the AC and see what it does. If that takes care of it, you're done. If not, there is a base idle adjustment that may have crud in it as well. The simple thing is to turn the screw out a quarter turn and see if that fixes it. The screw is near the throttle body in a round hole (sometimes it has a rubber cap on it). The screw is about 3/8 of an inch thick and is silver.