1994 Lincoln Mark VIII Engine

Forget the crankshaft and sensor. A problem with the crankshaft is really serious. You'd have lots of noise and low oil pressure. That won't last long before the engine seizes up. The engine won't run with a defective crankshaft position sensor.

A vibrating engine is due to a misfire. That can be due to worn spark plugs and wires, or less commonly it is due to a fuel supply problem. Start with the basics. Replace the spark plugs and wires if they haven't been changed in a while. If the problem persists, the next step is to determine if the engine is running rough because it is running too slowly, or if it's running too slowly because of a misfire. The Engine Computer will bring engine speed back up to the desired speed when there's a misfire, but it has a limited ability to do that.

Misfires are easy to feel at low speeds because there is such a long time between power pulses when the misfire occurs. At higher speeds there is so little time elapsed during the misfire that it is hard to notice.