Audi Q7 Engine Stalls: Fuel System Issues Exposed

I had similar fuel system issues with a 2015 Audi Q5 3.0 TFSI last year and being somewhat experienced with engine diagnostics, I recognized the symptoms right away. The engine stalling and rough running were definitely concerning. After taking it to a workshop, they discovered a faulty wiring connection to the fuel pressure sensor, which was causing incorrect fuel mixture readings. The repair involved replacing damaged wiring and reconnecting the sensor properly, costing 95 Euro for parts and labor. The engine knock stopped immediately after the fix, and fuel economy returned to normal. These symptoms definitely match what you're describing with your Q7. Before suggesting more specific solutions, could you share: What error codes are you getting exactly? Does the problem get worse when the engine is warm? Have you noticed any changes in fuel consumption? Are there any other warning lights besides the check engine light? This information would help determine if your issue is similar to what I experienced or if it might be something else in the fuel system.

Thanks for the detailed reply. My vehicle currently shows error codes P0171 and P0174 which indicate lean fuel mixture on both banks. The problem does worsen after the engine reaches operating temperature. At my last service at 17312 KM they checked the fuel quality and replaced the fuel filter as part of routine maintenance. Since then I noticed increased fuel consumption of about 15% compared to before. The only warning light currently on is the check engine light. I have not tried using any fuel additives yet, though I am considering trying some to see if they help clean potential deposits in the fuel system.

Having gone through this exact situation with my Q5, those error codes (P0171/P0174) strongly suggest a more serious issue than just the wiring problem I initially encountered. After further diagnosis on my vehicle, the root cause turned out to be carbon buildup in the combustion chamber, which is quite common in these direct injection engines. The increased fuel consumption you mentioned matches what I experienced. In my case, the carbon deposits were affecting the fuel mixture and causing poor combustion. This explains why the problem gets worse at operating temperature. While I initially thought cleaning additives might help, they provided minimal improvement. The permanent solution required a professional cleaning of the intake valves and combustion chamber. The total repair cost was around 450 Euro, but it completely resolved the lean condition and restored proper fuel economy. Before you proceed with additives, I would strongly recommend having a technician check for: Vacuum leaks around the intake manifold, Mass airflow sensor function, Carbon buildup on intake valves The fuel contamination issue you mentioned was ruled out since you recently had the filter changed. Based on my experience, these symptoms point more toward an air intake or carbon deposit problem rather than a fuel delivery issue.

Thanks for sharing your experience with P0171/P0174 codes. The fuel consumption increase and performance issues getting worse at operating temperature are definitely concerning. Similar to what you found with your Q5, I suspect I may be dealing with carbon deposits affecting the fuel mixture. Since my fuel filter was recently changed and fuel quality verified, I am now leaning toward having a professional inspection of the intake system rather than trying additives first. Given the symptoms and potential for engine knock if left unaddressed, I will schedule an appointment to have them specifically check for vacuum leaks, test the mass airflow sensor, and inspect for carbon buildup. The 450 Euro repair cost you mentioned seems reasonable if it fully resolves the lean condition and restores proper performance. I appreciate the detailed explanation of your diagnostic process and repair outcome. This helps me better understand what to expect when I take it in. I will update once I get a proper diagnosis and repair completed.