On a '91 Chevy Cavalier automatic what causes the excessive vibrating when the car is in Drive or Reverse but not when in Park or Neutral?

Answer 1

It sounds like your plug wires are grounded to the engine block. IE.... melted somehwere along the exhaust route and grounded, noticeable when you put it in gear......

I don't think so, i have a 1993 cavalier 2.2L auto, which does the same thing, i put new plug wires on it about a month ago, and it still has the same vibration.

I would check your motor mounts. I had a 90 Sunbird and now have a 91 Cavalier, both of which had this problem. When you pull up to a stop light the whole car vibrates rather aggressively, but is calmed when the car is put into park or neutral. In both cars the motor mounts were bad causing the motor to jostle inside the engine compartment, but when you are actually driving the engine is torqued against the mounts and ceases to rattle. On the 2.2 there are 4 mounts, Right Front (by the engine coolant overflow tank), Right Rear (right above the trans axle), Left Front (looks like a dog bone on the bottom by the radiator) and the transmission mount (on top on the left by the wheel well).

Last night I replaced the right front and right rear and this solved my problem.