Alright. So I own a 1994 Pontiac Grand Am with 101,000 miles currently. It has a 2.3 L 16-valve High Output Quad-4 in it. But for some odd reason it is terribly slow. Like 0-60 in 2 minutes. I took it to a mechanic and he said it was only running on two cylinders. The car is also difficult to start. But once it gets running it's good. Just slow and when you give it some gas it spews black smoke out the exhaust. I replaced the coil pack, spark plugs, spark plug wires, and I'm thinking of replacing the oxygen sensor next. Any suggestions?