The 2.0 Engine fitted to many of the VW range of vehicle has a common fault with eh PCV valve. The symptoms that come with this are erratic idle or what some people call hunting. The Idle can fluctuate from between 500 RPM (almost stalling) up to 2,000RPM without you touching the vehicle. This can sometimes, but not always give you a loud hissing noise or a vacuum leak noise too.
It is also important to note that the check engine warning light may come on with this fault but not always. that is to say that just because you don’t have a fault code logged does not illuminate the PCV as your culprit.
This can be diagnosed correctly by spraying some carby cleaner or brake cleaner around the PCV valve and seeing if there is a dramatic change in idle, if there is, the PCV is sucking air in after it is metered which is giving the idle fault. If the idle fluctuates with the spray, its time for a new PCV valve.
These valves are not to expensive and relatively easy to replace. Our advise is to stick with the genuine part from VW as its not very expensive and there are some discrepancies with the aftermarket options that can introduce problems to your VW. Be sure you get the rubber gasket with the new PCV.
If you do have fault codes for mass air flow meter, oxygen sensors, lean mixtures or manifold vacuum start by looking at the PCV valve as it is very common.
If you need any help with your VW feel free to contact us here.