bouncing RPM 1988 5.0 Five Speed

Hope someone can help with this problem. 1988 Ford Mustang 5.0 five speed. Sometimes the engine will start to loose power while idling. Turning on the air conditioner will start bouncing the RPM up and down until the engine shuts down. It just looses power but starts right back up with no problems. I have replaced all of the vacuum lines on the engine. Replaced the idle control and other engine parts. Checked the PCV valve. I have checked the air induction system and replaced the gaskets. Have replaced the fuel pump regulator and filter. I had the fuel injector system cleaned and computer system checked the read out showed no major problems. Replaced the brake booster.
Any suggestions appreciated.

Phil