Vibration throughout whole car when in D & R

[sneakygt91]

I am having a vibration throughout the whole car when I shift into reverse or drive. It only occurs when I am holding the brake and sitting still in either of those two gears. In neutral or park the motor idles perfectly and does not vibrate, only when I am holding the brake in R or D. I replaced the rubber transmission mount, but that only decreased it a little bit. I was then told it might be a plug or my plug wires breaking down under torque. I replaced the plugs and that didn't do any good. I have yet to replace the wires, but they are only about 5 years old. Any advice would be appreciated. BTW: 66 Mustang coupe, 200 inline six, auto trans

 

[candphall]

I would try motor mounts next

 

[10secgoal]

My guess would be lean or a miss if only in gear.

 

[sneakygt91]

any other suggestions? I am going to look into it this weekend and if I cannot solve the problem, I am just going to take it up to the Mustang restoration guy in town.