Read this on another site - worth a look!
There is a TSB on the motors, apparently they fail. VW apparently put a flap in the intake manifold that opens and closes to increase and decrease airflow to the cylinders.
If yours doesn't work, you get a code that says intake manifold runner control flap stuck open. You will notice two things with your car.
1. A loss of power. Not huge, but instead of your car accelerating quickly it accelerates slower and just gets louder.
2. At idle, the car does not have a steady idle, it goes up and down. Again, this is not severe, just not a smooth idle. Fluctuates 100 rpm or so, nothing major.
If the motor is fine, the problem could be - that there is a control arm that presses on two plastic pieces to open and close the flaps