Audi S8 Turbo Hiss Points to Vacuum Leak Troubles

As an A7 3.0T owner, I encountered nearly identical symptoms last year. The hissing sound combined with poor fuel economy and check engine light typically indicates an air intake leak, often from a cracked intake hose after the turbocharger. The issue required replacing the intake hose and checking the surrounding clamps and seals. The leak detection test revealed multiple small cracks in the rubber sections, likely due to heat stress from the turbocharger. This was causing unmetered air to enter the system, throwing off the air-fuel ratio and triggering the engine misfire codes. While not immediately dangerous to drive, leaving it unfixed can: Cause continued poor fuel economy, Put extra stress on the turbocharger, Lead to rough idle and potential engine damage Recommend getting it diagnosed with a smoke test to pinpoint the exact location of the leak. The repair itself is straightforward but requires careful inspection of all connecting components while the intake is exposed. Make sure they check the diverter valve and wastegate actuator while accessing the area. This is a known wear point on these engines, especially around the 45000-60000 km mark.

Thanks for the detailed response on the air intake leak issue. Your description matches my symptoms exactly, especially the part about the leak detection revealing multiple small cracks. I had the repair done last week and the hissing is completely gone now. Did you remember roughly what the repair cost was? Also wondering if you noticed any other issues with the intake manifold or air filter that needed attention while they were in there checking things out? The fuel economy seems back to normal now but looking to stay ahead of any related problems that might come up.

Just had mine fixed last month, the air intake system leak was indeed the culprit. Total cost was 100 Euro for replacing the cracked intake hose, which matches pretty well with what these repairs typically run. While they had it open, I had them do a thorough check of the throttle body and intake manifold, but everything else looked clean. The original air filter was still in good shape, though its worth monitoring since debris can get sucked in through these leaks. Good to hear your fuel economy is back to normal. These leaks can really throw off the engine management system and cause engine misfire issues if left unchecked. The repair should last a good while now, these upgraded hoses handle the heat stress much better than the originals. Just keep an eye on your check engine light and listen for any unusual sounds around the turbo area during acceleration. Regular inspection of the vacuum hoses and intake components during maintenance will help catch any issues early.

Thanks everyone for the help. I took it to a new shop last week and the experience was much better than my previous mechanic. They found the vacuum hose leak right away using their smoke test equipment. While fixing that, they also spotted a worn air filter that needed replacement. The whole repair including parts and labor came to 280 Euro. They showed me the cracked hoses and explained how the leak was affecting the engine performance. Really appreciated their thorough approach, they even checked the intake manifold and surrounding components while they had it open. The car runs perfectly now, no more hissing, check engine light is off, and fuel economy is back to normal. Will definitely keep up with regular inspections to catch any issues early. Lesson learned about not putting off these kinds of repairs when the symptoms first show up.