its the rear pcv pipe on the back of the engine, inside of it is a check valve, i bet thats bad, start there before assuming its the turbo.
http://www.ecstuning.com/Volkswagen-Golf_V--2.0T/Engine/Emission/PCV/ES9880/Breather Tube Gasket
Volkswagen Golf V 2.0T
Only needed if not replacing tube (ES#7511)