1989 Taurus Bad Engine Vibration

[longjohnc]

This is a 3.8 L. I took the Taurus into the shop to replace the water pump. Almost immediately after I got the car back the engine began to vibrate violently, especially at low rpms. At first I thought it might be the transmission, but the problem manifests when in Park. I took it back to the shop right away. They weren't sure what the problem was, but they talked me into a tune-up (which it probably actually needed). This did not solve the vibration problem. The shop said that it might be something in the transmission, torque converter, or harmonic stabilizer. I didn't have a lot of confidence in their diagnosis: why didn't they tell me that before they took my money for the tune-up? The vibration persisted, and things started shaking loose, like the exhaust pipe. Then we lost reverse. Then last Satruday night, while on the freeway, the serpindine belt fell off. Pep Boys replaced the serpendine belt on Sunday. On Monday, I took the car to a different shop to repair the transmission and to get their take on the vibration problem. As the transmission lost third gear as well as reverse, they rebuilt the transmission (and it is working just fine). They thought the vibration might be caused by the engine mounts, but they found that the mounts were in good condition. Then one of the mechanics thought that the vibration problem might be caused by one of the serpindine belt pulleys having its position changed during the water pump replacement. Today I went back to the shop that did the water pump; they disclaimed any responsibility, said that they could not possibly have changed any pulley positions, and, in any event, the vibration could not possibly be caused by changed belt pulleys. Since the transmission has been rebuilt and is working fine, they now tell me it must be the harmonic stabilizer. The engine vibrates at all speeds, more so at low rpms, and less so at freeway speeds. I would appreciate any help from the forum, please! Thanks.