My engine was recently rebuilt because a head had blown and needed to be fixed. The oil pressure gauge was flickering and eventually started getting to red and popping back up to normal while flittering around. I replaced the oil filter, and it was fine for a while, but now it's no dice. It's started doing it again, after two weeks, and this time it's worse. It doesn't do it all the time, just when idling in drive. I'm going to run some head gasket seal through the engine, but I doubt that helps the problem. Does anyone know what it could be?

 

Could just be low on oil. Or the sensor is bad. I'd suggest going back to where you got it and telling them to redo it.