I've seen the other posts but I can't quite fond one with the exact same problems so here's mine. When im idling (usually does it the worst with ac on) my oil pressure drops to half then 0 on stock gauge. Goes up of course when I rev up or accelerate. It doesn't do it as often if ac is off. My idle is 1000-1100 ac off and 900 with it on. I've replaced the sending unit. My next step is to check the pump seal and get a mechanical gauge. Does anyone have any other advice?