2002 Volkswagen Passat Vibrates at Idle

My passat has a problem where it vibrates when in gear when I have my foot on the brake (at Idle), once I accelerate the vibration goes away. Motor mounts have been recently replaced, and the dealership inspected the car and can find nothing wrong. I just want to know what tests of my own I could run to figure out what the problem is so I know what needs to be fixed. I have done some reading and think it could be anything from the balance shaft to misfiring cylinders to wrong idle speed or idle speed control. Any help would be appreciated.

02 vw passat sedan 1.8T 4 cyl engine.