Dear Doctor: I recently had my 2003 Buick LeSabre serviced at 96,000 miles, including oil change, tune-up, transmission fluid change and replacement of two motor mounts. Now, after this service the engine vibrates at idle. The mechanic replaced the mounts with another brand (neither replacements were GM) but the problem remains. Three individuals in the shop checked and could not find the cause. The tune-up and other work, along with the vibration dampener, were rechecked and found to be OK. Do you have any suggestions? Frank
Dear Frank: The first step is to have the technician pry the engine in any direction while you are sitting in the car and see if the vibration changes or goes away. This is the way we check engine-related vibrations. A vibration at idle can also be related to the wrong serpentine belt and or metal-to-metal contact in the exhaust. As for the aftermarket engine mount, the technician will need to make sure it matches the original. Some engine mounts are liquid filled and some aftermarket engine mounts lack quality and are not liquid filled.