The car has a fairly serious vibration at idle (750-800 rpm's) As soon as I come off idle it smooths out. Engaging the a/c, at idle, makes it worse. I have replaced all tune-up items and have changed the front torque strut and the driver's side motor mount with no success. I hear the rear motor mount is somehow, vacuum controlled. I did find a module mounted to the firewall that feeds engine vacuum to a small black canister mounted next the the mount. The module has an electrical connection and also has a rotary **** on top, which does not appear to change anything when adjusted. I think this module may be the key, but I have never heard of a vacuum controlled motor mount. Any ideas? Thanks.

 

Sounds like it could be a bad rear motor mount. Make sure the solenoid and vacuum lines are good. If they are, check to see if the lever on the back of the mount is moving when you energize the solenoid. (With the engine idling.)