Engine runs rough for only a five or so seconds when first started for the day. Then, engine light came on immediately. It runds smooth after being started the rest of the day and smooth on restarts. Then, after 3-4 days the engine light went out. On subsequent days it started up smoothly. Then, after about 10 days, the same thing happened, started up rough for a few seconds, then engine light came on. Ran smooth when driving and when restarting the same day. After 3-4 days, the engine light went out again and the car started each day smoothly. Then, yesterday, same thing all over again...started up a little rough in the morning and the engine light came on. Then runs smoothly the rest of the day, including restarts on the same day. I suspect the engine light will go out again in about three or four days and it will be smooth starting for 10 days or so. This keeps repeating itself. What could it be? Could it be an oxygen sensor? The car was totally serviced in April, six months ago. Only put 2000 miles on it since. The service included new plugs, new spark plug wires, new fuel filter, state inspection, etc. It's been a great car this 1999 Pontiac Bonneville, 6 cylinder.
Nov 3, 2010 at 7:13 PM