Volkswagen 2.0L turbo, system lean condition, will not idle, rough idle, check engine light on. Here’s a list of the possible codes that will set and their descriptions.
- P0300-P0304 – Cylinder misfires
- P0171 – Bank 1 system too lean
- P0507 – Idle air control sys. RPM higher than expected
This vehicle sets the fuel trim system lean and idle control system codes with no misfire codes yet but they will eventually set misfire codes also. Usually the P0300 random cylinder misfire will set first. The crankcase has to be sealed properly or the engine will develop an internal vacuum leak. In this situation the cam plug popped out causing the symptoms on this vehicle. A severe oil leak, yes but the engine ran like crap. These engines are very sensitive to crankcase pressure, similar to the BMW engines. The most common problem that causes the same symptoms is the PCV valve or aka pressure regulator crankcase vent valve . The valve bolts to the valve cover with two hoses connected to it.
Volkswagen has updated this part multiple times and has put out plenty of technical service bulletins explaining the failure and updates. We also replaced the valve as part of the repair since they fail so often. Replaced the camplug, cleaned residual oil, cleared codes and retest. Engine runs great now with normal fuel trim values. The diagnostics testing is as simple as blocking the hoses to the PCV valve, start engine and monitor fuel trim. You will also notice the idle will immediately return to normal. So if you run into this problem you know what to check just make sure it doesn’t have a large crankcase leak tricking you into thinking the PCV valve failed. Good luck on your repairs! Please leave any questions or comments on the comment form below , thanks for reading.