VW Touran Diesel: Fuel Economy Drop & Power Loss Fix

I had a very similar issue with my 2017 VW Tiguan diesel last year. Having some experience with diesel engines, I recognized those symptoms immediately. The increased fuel consumption combined with power loss initially pointed toward fuel injector problems, but it turned out to be a consequence of a clogged air filter that damaged the turbocharger. The engine knocking was actually caused by the turbocharger not functioning properly due to the restricted airflow. The workshop diagnosed this during a routine inspection, I got lucky since the damage was caught early before it could affect the crankshaft or cause more serious engine damage. Since the original issue was covered under warranty (faulty filter housing seal), the turbocharger replacement was also covered at no cost. To better assist with your situation, could you provide: Current mileage, Service history details, Any recent repairs or maintenance, Whether the engine knocking occurs more during cold starts, If there are any specific error codes showing The symptoms are quite similar, but these details would help determine if you are facing the same underlying issue. Would strongly recommend getting it checked soon, as running with reduced power could lead to more extensive damage.

Thanks for sharing your experience. My last service was 4 weeks ago where they replaced the spark plugs and did a routine inspection. The knocking is definitely more noticeable during cold starts. Just checked the error code with my OBD reader, it shows P0299 which points to turbo underboost. The piston rings and head gasket were never replaced during my ownership. Given the symptoms match what you described, I will have the air filter checked first before investigating other components like the turbocharger or camshaft assembly. My main concern is this developing into a bigger issue affecting engine compression if left unchecked. Will book it in for diagnosis next week.

Thanks for the additional details. The P0299 code definitely aligns with my experience, it is the exact same code I got before discovering the clogged air filter and turbo damage. Since your issue is showing identical symptoms and error code, there is a good chance you are dealing with the same root cause. Given the cold start knocking, checking the air filter and turbocharger assembly should be the first step before investigating potential head gasket or fuel injector problems. In my case, the turbocharger damage occurred because dirt particles made it past the compromised air filter housing. The restricted airflow put extra strain on engine components, particularly affecting the timing belt tension and turbo operation. While the head gasket and crankshaft were thankfully unaffected in my situation, running the engine with turbo underboost for extended periods could lead to more severe issues. The workshop should be able to diagnose whether your turbocharger can be rebuilt or needs replacement. Good call on scheduling it for next week. This type of issue tends to worsen quickly if not addressed, potentially leading to reduced compression and damaged internal components.

Thanks for the detailed explanation. After researching P0299 turbo underboost issues, I feel more confident about the likely cause. The timing of the engine knocking starting after the recent service is interesting, I wonder if something was overlooked during the spark plug replacement that could have affected the air intake system. I will prioritize having them inspect the air filter and turbocharger next week. Your experience helps confirm that catching it early before it causes timing belt or head gasket damage is crucial. The last thing I want is a complete engine rebuild if internal components get damaged from running with insufficient boost pressure. I have noted down all the symptoms to explain to the workshop, the cold start knocking, increased fuel use, power loss, and error code. Hopefully addressing the air filter and turbo situation resolves it like in your case rather than indicating more serious camshaft or compression problems. Will update once I get the diagnosis.