vibrating at idle
 

Hi again ! the flywheel has a ring of teeth around it fanning outwards ( like daisy petals ) this is the means that the engine is turned by the starter motor to start the engine . If one is missing or chipped ( part of the tooth is missing ) , the flywheel is out of balance by one tooth / chip - by diameter of the flywheel and the crankshaft will vibrate , this MAY be the cause , and the fluid in the torque converter may be compensating by moving at greater speed to offset the imbalance , it's only a theory but may also be worth checking by getting underneath the car and removing the plate at the rear of the engine / transmission and turning the crank 360 degrees to check for a missing tooth / chipped tooth .

Has it been vibrating like this since you bought it w/20K miles? If not, when did the vibration start (and did it follow any maintenance or unusual event you can recall)?

No the vibration started about 3 years ago and I had several shops try to diagnose the problem with no luck. Nothing changed that I could point toward as a cause.

Again, please post up the results of the compression test. At this point, that seems to be the most appropriate next troubleshooting step.

It could be a clogged injector as well. Or maybe a bad one. In reality it could be anything. But the moderator is right. without test results of com, tests, injector sets and using all the diagnosis tools available it is impossible to diagnose your car. If you told us what test were performed by the mechanics that have already looked at the car. That would be helpful. Very helpful.