RS7 Intake System Issue Causing High Fuel Usage

Dealt with a very similar issue on my 2011 RS6 last year, and I have some experience working on these engines. The symptoms you describe match what I encountered, increased fuel consumption, hissing noise, and check engine light. In my case, it turned out to be a cracked vacuum hose connected to the air intake system. The throttle body wasnt getting proper readings due to the leak detection system picking up unmetered air. The repair was straightforward, the workshop found the leak using smoke testing, replaced the damaged air intake hose and performed a thorough inspection of the surrounding components. Total cost was around 100 Euro including diagnostic work. The difference in performance was immediately noticeable after the fix. Could you share: Current mileage? Any other unusual sounds or performance changes? Have you recently replaced the air filter? Any modifications to the intake system? This information would help determine if your issue is similar to what I experienced or if there might be other factors to consider.

Last service was done 2000km ago where they replaced the air filter, but the fuel economy issues started recently. The turbocharger and intake manifold were inspected during that service with no issues found. After the symptoms you described, I also noticed the engine feels a bit rougher at idle. No modifications have been made to the air intake system, everything is stock.

Thanks for the additional details. Based on what you described, it sounds very similar to my experience, especially the rough idle, I forgot to mention I had that too with my RS6. The recent air filter change rules that out as a cause, but the rough idle combined with the hissing suggests the vacuum leak might be more significant than what I initially dealt with. Mine was a small crack, but larger splits can develop over time, especially near connection points in the vacuum hose system. After my repair, I learned these cars commonly develop leaks where the throttle body connects to the intake manifold. While your manifold checked out during service, the seals and gaskets between components could have deteriorated since then. Our engines use a sophisticated leak detection system, and any small breach in the air intake path can trigger these symptoms. Since youre getting multiple indicators, the hissing, rough idle, and increased fuel consumption, Id suggest getting it checked soon before it potentially affects other components. Cost-wise, if its a similar issue to mine, you might be looking at 150-200 Euro depending on which specific components need replacement. The diagnostic process should be similar, smoke testing usually reveals these leaks pretty quickly.

Current mileage is 85000km. The rough idle is more noticeable when the engine is cold, and it seems to smooth out a bit after warming up. The hissing gets louder when accelerating hard. Your experience sounds exactly like what Im dealing with, particularly the leak detection system throwing off the readings. The workshop availability is next week, but Im relieved to hear this is likely just a vacuum hose or connection issue rather than something more serious with the intake manifold or turbocharger. Ill make sure they do the smoke test to properly identify the leak location. Quick question, after your repair, how long did it take for the fuel economy to return to normal? And did you notice any immediate improvement in the engine running smoother at idle? Thanks for sharing your experience. It helps to know what to expect when I take it in.