VW Sharan Turbo Issues: Boost Pressure Problems Fixed

I had a similar issue with my 2015 VW Touran last year, and as someone with moderate experience working on diesel engines, I can share what worked for me. The symptoms you describe match exactly what I experienced, poor engine performance, significant turbo lag, and increased fuel consumption. After diagnosis, the problem turned out to be a faulty bypass valve, specifically the vacuum switching valve that controls boost pressure. The repair involved: Complete diagnostic scan, pressure testing of the vacuum system, replacement of the vacuum switching valve, system recalibration. Total cost was 140€ including parts and labor. After the fix, engine performance returned to normal and the boost control worked perfectly again. Before jumping to conclusions though, could you share: Any specific error codes from the diagnostic scan? Does the boost issue occur at specific RPM ranges? Have you noticed any unusual sounds from the engine bay? When was your last routine maintenance? This would help determine if your issue is identical to what I encountered. There could be other vacuum leak sources affecting the turbo system that need investigation.

Last service was done at 11254km. After getting OBD codes read, they showed P0299 and P0234. Engine consistently makes a slight whistling sound near the turbo area when accelerating. The boost solenoid appears functional when tested, so I am leaning towards a vacuum leak around the intake manifold area. The engine does pull decently until about 2000 RPM, then loses significant power. Will check vacuum lines and pressure sensor connections before deciding on parts replacement. Has anyone found a reliable way to pinpoint vacuum leaks in these particular engines?

Thanks for the additional details. Having dealt with similar codes on my Touran, the symptoms you describe sound very familiar, especially that whistling noise and power loss above 2000 RPM. After my initial repair with the vacuum switching valve, I actually discovered a small crack in the intercooler pipe that was causing compressor surge under load. This explains why the boost solenoid tested fine but problems persisted. For finding vacuum leaks, I used a smoke test which revealed several issues: Cracked intercooler pipe near the turbo connection, Deteriorated vacuum line to the wastegate actuator, Loose clamp at the intake manifold The complete fix required: New intercooler pipe (85€), Vacuum line kit (35€), New clamps (12€) After addressing these points, the engine performance returned completely, with proper boost response and no more abnormal sounds. The pressure sensor readings also stabilized once the system was properly sealed. Since your symptoms match so closely, I would strongly recommend checking those same components, particularly given the P0299 code indicating underboost conditions.

Thanks for sharing those diagnostic codes and symptoms. Based on both the responses and my own situation, I feel more confident about tracking down the issue. The whistling sound combined with the power loss above 2000 RPM definitely points toward boost control problems. A smoke test seems like the smart next step to check for vacuum leaks before replacing any major components. The pressure drop and turbo lag issues others described mirror my symptoms exactly. I will inspect the intercooler pipes, vacuum lines, and boost solenoid connections carefully since these appear to be common failure points. The total repair costs shared here seem reasonable, around 130-150€ for parts if multiple components need replacement. At least I now have a clear diagnostic path to follow rather than just guessing at the problem. Will start with a thorough inspection of the intake system for any obvious vacuum leaks before moving forward with parts replacement. Once again, this has been very helpful for narrowing down the likely causes. Time to get started on the diagnostic work.