VW Sharan Misfires and Power Loss Due to Fuel Mix Issue

Had nearly identical symptoms with a 2015 VW Touran TSI last year. The check engine light came on and the engine started running rough, especially during acceleration. As someone with moderate experience working on VW engines, I initially suspected the oxygen sensor, but it turned out to be a faulty fuel injector. The workshop diagnosed it by testing the fuel injection system and found one injector was not spraying properly, affecting the air-fuel mixture. They had to replace the defective injector and clean the throttle body while they were at it. Total repair cost was 515€, including parts and labor. The whole job took about 4 hours at the shop. Since the repair, the engine has been running smoothly with no misfires or power issues. The check engine light hasn't returned either. Before suggesting specific fixes for your case, could you share: Current mileage on your Sharan? When was the last time you had a fuel system cleaning service? Are you using regular or premium fuel? Have you noticed any unusual sounds or vibrations? Does the problem get worse when the engine is cold or warm? This information would help determine if your issue is similar to what I experienced.

Thanks for the response. My Sharan has 62115km on the odometer, and these symptoms started about 2 weeks after my annual service. The mass air flow sensor and EGR valve were actually cleaned during that service. I noticed the misfire gets worse when the engine is warm, especially under load. No unusual sounds, but definite jerking during acceleration. Have also noticed slightly higher fuel consumption lately. Based on your experience with the injector issue, I might get those tested first. Were there any warning signs before your injector completely failed?

Thanks for the additional details. Unlike my injector problem which showed up suddenly, your symptoms following a recent service and getting worse when warm point to a different potential cause. In my case, I had noticed slightly rough idling about a week before the injector completely failed, but nothing as progressive as what you describe. The mass air flow sensor in your case was recently cleaned, but the symptoms you mention, especially the increased fuel consumption and misfiring under warm conditions, still align with potential MAF sensor issues. Since my initial injector repair, I learned these VW engines can sometimes show false clean readings even after a MAF sensor cleaning. The sensor might pass visual inspection but still send incorrect readings to the ECU, causing the air-fuel ratio to run lean. Consider having the throttle body thoroughly checked too. In some cases, cleaning can disturb carbon deposits, which then settle elsewhere in the intake system. The check engine light and performance issues you describe match this scenario pretty well. Based on the mileage and service history you shared, I would recommend: 1. Getting the mass air flow sensor tested, not just cleaned 2. Having the oxygen sensor readings verified 3. Running a complete fuel injection diagnostic These tests should reveal whether your issue matches my injector problem or points to something else in the air-fuel delivery system.

Thanks for the input. After reading about similar experiences, I decided to take my Sharan to a VW specialist workshop today. They ran diagnostics and found both a faulty mass air flow sensor and a partially clogged catalytic converter, a combination that was causing the lean condition and misfires. The MAF sensor was giving incorrect readings despite the recent cleaning, exactly as suggested. They also found the catalytic converter had started breaking down internally, restricting exhaust flow when hot, explaining why the problems got worse with a warm engine. Total repair cost came to 890€ including: New mass air flow sensor, New catalytic converter, Labor and diagnostic fees The car now runs perfectly, no more jerking or misfires during acceleration. Fuel consumption has returned to normal too. Really glad I got this sorted before it caused more damage. Will definitely keep a closer eye on the air-fuel ratio indicators going forward. Thanks again for helping point me in the right direction with the diagnosis.