The idle stabilizer is the likely culprit. The computer sends a signal to it to vary it's dwell (it is a rotary valve that flips open/closed at a specific rate). When you turn on the A/C, the idle stabilizer is supposed to spend slightly more time open, increasing the idle speed (same with when it's cold). They gum up and stick. Locate this device. On the 2.3 8V, it is between intake runners 3 and 4. Remove it. Spray carb cleaner in one of the air connections while holding your hand over the other. Shake and repeat. Poke something plastic (soft) into it and make sure the valve is free to move. Plug the valve back in and turn the ignition on (dont start the engine). You should see the valve flip back and forth. If not, meter the connections. You should see voltage come up, then drop. If not, the computer, or one of it's inputs (temperature sensor probably) is faulty.