The entire drivetrain of the Jetta 2.0 is held to the car by three rubber-isolated mounts. Two mounts are located on either side of the upper engine bay, and the remaining mount secures the mount below. Over time, the rubber bushings inside the mounts break down and tear, resulting in increased movement and drivetrain vibration.
In this article, we will focus on the lower engine mount. This mount counteracts the engine's front and back movement when accelerating and decelerating. If you notice a hard knocking sound under heavy acceleration, it is possible that the mount may be going out.
A good test is to have a helper rev the engine while you watch it with the hood open and the car in neutral. If there is excessive front and back movement, there is a good chance the mount is bad and needs to be replaced.
Note that replacing the mount requires you to jack the front of the car up and secure it on jack stands. See our article on Jacking up Your Mk4 Jetta for more information.
Once the car is secured on jack stands, loosen and remove the two 16mm bolts (green arrows) securing the mount to the engine. Now loosen and remove the two 13mm bolts (purple arrows) securing the mount to the frame rail. Carefully lower the old mount out of the way.
And here's the finished result with the mount removed from the engine. Installing the new mount is the reverse order of removal.