RS7 Fuel Consumption Issue Points to VANOS Problem

I had a similar issue with my 2016 RS6 last winter. I have some experience working on cars, mainly basic maintenance, but I leave the complex stuff to professionals. The check engine light came on during highway driving and I noticed the engine felt less responsive, especially during acceleration. Fuel economy took a hit too. My workshop diagnosed a faulty inlet camshaft VANOS solenoid, which was affecting the variable timing system. The repair took about 4 hours and cost me 250 Euro including parts and labor. The mechanic explained that the VANOS solenoid had accumulated debris over time, disrupting the proper timing control. They replaced the solenoid and cleaned the surrounding components. Before suggesting specific solutions for your RS7, could you share: Current mileage, Any unusual engine sounds, Whether the issue occurs more during cold starts, If you have access to the specific error codes, Service history regarding timing chain maintenance This information would help determine if your symptoms match what I experienced and whether you might be facing a similar VANOS solenoid issue.

My current mileage is 171477 KM, with the last full service done in June. The engine does make a slight rattling sound during cold starts, which I forgot to mention. The error code reads P0011, which from what I understand relates to inlet camshaft timing. The timing chain maintenance is all up to date according to service records. The low power issue seems most noticeable when accelerating from a stop, which matches what you described with your experience. The variable timing problems you mentioned sound very similar to what I am experiencing. Your repair cost sounds reasonable. Did you notice immediate performance improvement after the VANOS solenoid replacement?

The improvement after the VANOS solenoid replacement was dramatic and immediate. The engine response became much crisper, especially during initial acceleration, and fuel consumption returned to normal within the first tank. That P0011 code combined with your cold start rattle strongly suggests VANOS failure, just like my case. The symptoms are nearly identical, the low power issue during acceleration and increased fuel consumption are typical signs of inlet camshaft timing problems. My repair actually turned out to be a good preventive measure too. The mechanic found that addressing the VANOS issue early prevented potential damage to the timing chain components. Given your mileage and symptoms, I would strongly recommend getting it checked soon to avoid more extensive repairs. One key difference to note, my repair was relatively straightforward because I caught it early. The rattling sound you mention could indicate more debris accumulation in the VANOS system than I had, which might affect the repair time and cost. Still, even if more extensive cleaning is needed, it should be a manageable repair. Have you noticed any change in the intensity of the cold start rattle over time?

The cold start rattle has definitely gotten more noticeable over the past few weeks. Thanks for the detailed insights, this really helps confirm my suspicions about the VANOS solenoid being the culprit. The timing matches what you experienced too, as my symptoms also started with slightly rough performance that gradually got worse. Your point about catching it early makes sense. Given that the timing chain maintenance is current and the error code specifically points to camshaft timing, I feel more confident heading into tomorrow's diagnosis. I will specifically ask them to check for oil sludge buildup around the VANOS components, since that could explain the increasing rattle noise. Knowing that you saw immediate improvements after the repair is encouraging. Based on your experience and the similar symptoms, I will go ahead with the VANOS solenoid replacement if that is what they recommend. The potential to prevent more serious engine misfire issues down the line makes it worth addressing now rather than waiting.