2005 VW Jetta P2279 and P0300-P0305 Fault Codes: Diagnosis and Intake Leak Investigation
My 2005 VW Jetta is showing fault codes P2279 and P0300 through P0305. I've already replaced the spark plugs, coils, and purge valve with no improvement. The valve cover has also been replaced. The check engine light activates only during hard acceleration in lower gears. A timing chain issue was suggested, but there are no related faults for camshaft position or adjustment components. I have not detected any leaks between the Mass Air Sensor (MASS) and the throttle housing or intake manifold. Propane testing has also shown no signs of a leak at the crankcase seal. Given these symptoms, I suspect an intake system leak—particularly around the engine side of the mass airflow sensor or in the air duct—but I'm unable to locate it definitively.
Could you please share your fuel trims (LT+ST) at idle and at 250-300 RPM?\nPotential causes for P2279 include:\n- Leak between the engine side of the Mass Airflow Sensor (MASS) and the air duct\n- Air duct leak on the engine side\n- Leak at the intake air temperature sensor\n- Throttle body or intake manifold crack/leak\n- Disconnected or broken vacuum hose\n- Faulty fuel injector seal at the intake manifold\n- Leaky brake booster vacuum hose\n- Vacuum leak under dash from a vacuum-operated device\n- Stuck PCV valve\n- Stuck crankcase oil filler cap\nAny component connected to the intake manifold could potentially trigger this code.\nFor more details, see: P2279 diagnosis and repair guide