91 volvo stalls at anytime

Its driving me crazy. i have 91 volvo turbo that will stall at any given moment. Highway , local roads, it dosen't matter. It will drive smooth for a day then stall the next. I have to stop and wait thirty seconds then it will start up fine. I totally lose rpm and engine power, electric is fine. Tried fuel injection cleaner it made problem worse, stalled three times coming home from work.. started up fine next morning drove to work no stalling. Temp guage dances from middle position to low position when idling then stays in low position while on highway. Check engine light comes on for a couple days then turns off. Help me please, no time or money for multiple trips to mechanic. Took it once and mechanic couldnt see anything wrong with the car.