Volkswagen 2.0L Turbo P0171 P0507

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.

    Pressure Regulator Crankcase Vent Valve

    Pressure Regulator Crankcase Vent Valve

    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.


    VW Camplug Hole

    Camplug removed from camshaft retainer


    VW 2.0L turbo camplug popped out


This post was written by: Martin Hand


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About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.

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