The 1.8T engine has a one way check valve that can become stuck
due to PCV sludge. This check valve is located under the intake
manifold next to the big plastic PCV elbow that is mounted to the
You should see a "T" junction. This is where that one-way check
valve is located.
Another common component to get plugged-up, is the "suction-jet
pump" (image attached).
It is molded to plastic hoses. So it is best to replace it complete
with all the piping attached, or you can use a heat gun and soften
the molded tubes, remove the tubes and then transfer them over to
the new pump.