[Bob Johnson]

It is very useful to isolate where the vibration is located. Does the vibration occur only when the car is in motion. If you rev the engine with the car stationary does the vibration occur when you quickly let off the gas? If it does not occur with the car stationary then it is likely a problem in the drive train. If it does occur with the car stationary then it is likely in the engine. Have you disconnected the fan belt? If so did the vibration go away?

Bob