Not related to any accident, the passenger side motor mount, nearest the crankshaft and other pulleys, can fail internally and cause vibration when idling in gear, such as when stopped for a traffic light. Putting the selector into neutral will in most cases relieve the vibration. As I understand the mount has a liquid-filled 'capsule' internally that somehow fails, and allows the fluid to disperse and then you get vibration. There are multiple OEM and aftermarket mounts for that spot at Rock auto's web site. I replaced the one in my mariner, and it definitely helped with the vibration, which had worsened over time. Not at all difficult once you place support under the engine(a good sized block of wood to spread the load on the oil pan seems to work adequately, though Ford says never use the pan as a support...
You will need metric sockets, a breaker bar/torque wrench, and at least a 12" extension, IMO. It is an unbolt-bolt-in-the-replacement type with no real technical skill necessary.
tom
