1994 Pontiac Grand Prix idling rough

Its the 3.4. Car just shut off when turning a corner. Restarted it moved 5 ft and shut off. Cranks fine. It has the idling problem known on these cars-revs up then down, up, down. The fix? Intake manifold or O2 sensor? Anyway I think its separate from that problem. I tried restarting the car tonight, one night later from the problem and it went with almost full pedal and idled with that pedal position. Rough, real rough, gray smoke out the back. It ran around 2K rpm's if I pushed the gas anymore I thought it would quit. Idled it for about a minute and took my foot off the gas=died. Im really not even sure if it would start again? I found some oil on the plugs too. Haven't tested them yet however. Thanx for the help!