VW Phaeton TDI: Throttle Issues Spike Fuel Consumption

Had a similar issue with my VW Passat 3.0 TDI from 2010. Being somewhat experienced with diesel engine issues, I recognized the symptoms immediately, especially the irregular throttle response and increased fuel consumption. The engine idle was unstable and the car throttle response felt delayed. Initially thought it was just a dirty throttle valve, but the workshop diagnosed a defective accelerator pedal module. They confirmed this by checking the electrical signals from the pedal sensors. After replacing the module, the throttle control and air intake system worked perfectly again. Total repair cost was 205€, which included diagnostics and parts. Fuel consumption returned to normal within the first tank. Before suggesting more specific solutions, could you share: Any warning lights on the dashboard? Does the engine management light come on? Have you noticed any unusual sounds when pressing the accelerator? Did the issue develop gradually or suddenly? This could help determine if your issue matches what I experienced or if its something else in the throttle control system.

Thanks for the feedback. No warning lights showing on the dashboard. The throttle valve issue started gradually over the last 2000km. Engine runs smoothly at idle but gets rough when accelerating. Had my last service at 15000km where they did basic maintenance but didnt check the throttle control system. The irregular engine throttle response seems most noticeable during cold starts and highway driving. Fuel efficiency has dropped significantly, using about 2.5L more per 100km than usual. No unusual sounds from the accelerator, just the delayed response time. Could cleaning the throttle body be a good first step before replacing components?

Based on your description, your symptoms differ slightly from what I experienced with my VW Passat. While my issue was related to the pedal module, your symptoms, especially the rough acceleration and cold start behavior, point more toward a dirty or failing throttle body. The gradual onset and lack of warning lights matches with carbon buildup in the throttle valve assembly rather than an electrical fault. This affects the air intake flow and creates the hesitation you are experiencing. Professional throttle body cleaning would be a smart first step, typically costing around 150€ including labor. However, if cleaning doesnt improve the engine throttle response, we might be looking at a faulty throttle position sensor or worn throttle valve components. My mechanic mentioned these components often start showing issues around your mileage in TDI engines. Before spending money on parts replacement, I suggest: Get the throttle body cleaned and inspected, Have the workshop check the throttle position sensor signals, Request inspection of the air intake system for other restrictions The cost difference between cleaning versus replacement is significant. A new throttle body assembly can run 400-600€ installed, so starting with cleaning makes sense given your symptoms.

Thanks for the detailed information. After hearing about your experience with a similar issue, I think I will start with the throttle cleaning option first. Your explanation about carbon buildup affecting air intake flow makes sense, especially since my problems developed gradually without warning lights. I have already contacted a local workshop to schedule a professional throttle valve cleaning service next week. They quoted 145€ for a complete throttle body cleaning and diagnostic check. If the throttle cleaning doesnt resolve my fuel efficiency issues, I will follow your advice and have them inspect the throttle position sensor and overall air intake system. The significant cost difference between cleaning and full replacement definitely makes it worth trying the less expensive option first. At least this way, I will know for sure if the poor engine throttle response is due to carbon buildup or if I am dealing with a more serious component failure. Will update once I get the results from the cleaning service. Hopefully, this solves the irregular throttle response and gets my fuel consumption back to normal levels.