Q: Poor idling, hesitation on acceleration, and oil on spark plugs.

Hello. From what you describe, it would appear that your vehicle may be experiencing more than one issue. Oil on the spark plugs can be caused by a few different things. If you also found oil in the spark plug tubes, then it may be possible that the valve cover gaskets or spark plug tube seals have begun to leak allowing oil into the tubes.

In some cases, the oil can work its way past the threads into the cylinder. You also mention, however, a loss of performance as well as smoke in the exhaust. This can be caused by oil getting into the cylinder, usually due to engine wear.

If the engine piston rings, or the cylinder head valve stem seals wear out they can allow oil into their respective cylinders. This could explain the oil on the plugs, the smoking, and even the loss in performance, if the issue is related to the piston rings.

A compression test would be the best way to determine if this may be the case. The battery terminal will also need to be taken care of before the engine can be restarted again.

In some cases, a poor battery connection can affect engine performance, however, it will not cause oil on the spark plugs or smoke from the tailpipe. I would also check the opposite terminal, as well as both battery cables to see if they may be corroded or in need of replacement as well. If you would like to have a professional scope this out, a certified technician from YourMechanic, can come to your car’s location to inspect the rough idling, hesitating acceleration, and oil leak to figure out what repairs are needed.