I have a 2001 Galant (4cyl) with 69,000 miles. I recently had the timing belt changed as regular maintenance. When I got the car back there was a vibration at about 1000rpm whether I was stopping or accelerating. It was suggested to me that the timing belt was not installed correctly, so I asked my mechanic to check it. He wasn't happy, but he took it apart and checked the timing marks and showed me that they were right on the money. The car still vibrates at 1000rpm. My mechanic said there might be an intake manifold leak, but the computer does not indicate a lean code. The vibration still feels like something is out of balance, but I have no idea what it is. You can feel the vibration through the steering wheel, and any passengers can feel it also. Can anyone help????

might be your engine/tranny mounts.

I had a similar problem with my galant. It sounds like it might be your engine mounts. The mounts have a rubber center that absorbs the engines vibration. In my case, this rubber portion of the mount was damaged causing the vibration and poor acceleration.