Stalling at idle especially in reverse or with the A/C on?

Vehicle listed above stalls at idle but mostly at low speeds in reverse or with the A/C on. I bought the van and drove cross country pretty well, now it has issues. At stoplights it seems like the van is in a very low idle, the oil gauge fluctuates very low the battery fluctuates and the lights on the dash and front headlights dim with the fluctuations. Van will shut off but turn on instantly usually just to shut off again, I had a shop replace the IAC valve but nothing else but have had alternator and starter replaced within last year or two, I also went through and cleaned the Injectors and cylinders with a toothbrush. Any ideas on how i can get this thing to idle without stalling again?