VW Caddy Diesel Performance Issues and Rough Running

I had a very similar issue with my 2013 VW Transporter diesel. Having some experience with diesel engines, those symptoms immediately sounded familiar. My engine also had reduced power, rough running, and jerking during acceleration. The fuel injectors turned out to be the root cause. One of them was defective, causing irregular fuel delivery and messing up the air-fuel ratio. The workshop diagnosed it using specialized diagnostic equipment to test the injection patterns. The repair involved replacing the faulty fuel injector and having the injection system recalibrated. Total cost was 515€ for parts and labor. Since the fix, the engine has been running smoothly with no power issues. To help diagnose your specific case, could you share: Current mileage on your Caddy, Whether the issues started suddenly or developed gradually, If you notice any black smoke from the exhaust, Any other warning lights besides the check engine light, Whether you've recently changed fuel suppliers or quality These details would help determine if your symptoms match what I experienced with the injector issue or if it might be something else like a clogged fuel filter or problematic oxygen sensor.

Thanks for sharing your experience. My Caddy has 78463km and was last serviced 2 months ago. Your injector theory makes sense, but I am also suspecting the mass air flow sensor might be the culprit. The issues started gradually over the past few weeks, and I have noticed the engine runs particularly rough when cold. No black smoke visible from the exhaust, but the check engine light started flashing before staying constantly on. The EGR valve was actually replaced during the last service, so I doubt that is causing problems. The throttle body might need cleaning as well since the idle is quite unstable. Has anyone checked if these symptoms could be related to the oxygen sensor?

Thanks for those additional details. When my VW Transporter showed similar symptoms, I initially thought it was the mass air flow sensor too, but after checking with my scan tool, the readings were normal. The unstable idle and rough cold running you mention are actually quite telling. While my injector issue caused similar problems, your symptoms align more closely with a faulty oxygen sensor combined with a dirty throttle body. The gradually worsening performance matches this scenario, especially since your EGR valve was recently replaced. In my case, before discovering the bad injector, I first cleaned the throttle body and replaced the oxygen sensor as preventive maintenance. While this helped the idle slightly, it did not solve my main power issues. However, given your specific symptoms, particularly the unstable idle and gradual onset, I would strongly recommend having both the throttle body and oxygen sensor checked first. The clean throttle body should help restore proper air-fuel ratio control, while a properly functioning oxygen sensor is crucial for the engine management system to maintain optimal fuel mixture. These are typically less expensive fixes compared to injector replacement. Would you be able to get a diagnostic scan to check for specific error codes? This would help confirm whether we are looking at oxygen sensor readings or fuel delivery problems.

Thanks for the input. After reviewing the suggestions, I will get both the throttle body and oxygen sensor checked first. The symptoms do seem to match what others have described, especially the idle issues. Just got the diagnostic scan done at a local shop. Error codes point to the oxygen sensor, with some additional codes related to the fuel system. The technician also noticed the throttle body was quite dirty when inspecting it. They quoted 380€ for replacing the oxygen sensor and cleaning the throttle body thoroughly. Will proceed with these repairs first since they are less expensive than replacing fuel injectors. The gradually worsening performance and cold running issues really do suggest these components might be the main culprits. If these fixes dont solve the problem completely, I will look into having the fuel injectors tested as suggested. Will update once the repairs are done in case anyone else runs into similar issues with their diesel engine.