Loud Hissing SQ7 Points to Turbo/Intake System Issue

I had similar symptoms with my 2019 S5, hissing noise, poor fuel economy, and a check engine light. After proper diagnosis, it turned out to be a cracked vacuum hose connected to the intake manifold. The symptoms match your description perfectly. The hissing noise occurs because the engine is pulling in unmetered air through the leak, which also explains the decreased fuel economy as the engine management system cant maintain proper air-fuel ratios. The repair involved a thorough smoke test of the intake system to pinpoint the exact location of the leak. In my case, the main issue was a deteriorated rubber hose that had developed hairline cracks from engine heat exposure. The fix required replacing the damaged vacuum hose and checking the throttle body connections. This is a serious issue that needs prompt attention, as continued operation can lead to running rich fuel mixture and potential damage to other components. The turbocharger system is particularly sensitive to incorrect air-fuel ratios. Recommend getting a proper pressure test done at a specialized VAG workshop where they have the correct diagnostic equipment for these specific engines.

Thanks for the detailed response about the vacuum hose issue. My problem turned out to be almost identical. The air filter housing had also collected quite a bit of debris which was restricting proper air flow, causing the engine misfire codes to pop up. Quick question, do you recall roughly how much the full repair cost? Also wondering if youve had any similar issues crop up since getting it fixed? Worth knowing if I should keep an eye on anything specific going forward with these engines.

Thanks for asking about the follow-up costs. After getting it properly diagnosed and fixed, the air intake system leak was completely resolved. The total repair came to 100 Euro for replacing the faulty intake hose. The leak detection test confirmed there were no other issues in the system. Its been running perfectly since the repair with no engine misfire codes or vacuum hose problems. The air filter housing inspection is now part of my regular maintenance routine to prevent debris buildup. A proper air intake system check during scheduled maintenance can catch potential issues early. One tip: if you notice any unusual hissing sounds or changes in fuel economy, get the vacuum hoses checked right away. These symptoms often point to developing air intake problems that are easier to fix before they affect other engine components.

I really appreciate everyones input here. Following up on my repair experience, took it to a different shop that specializes in performance vehicles. The diagnosis confirmed a split vacuum hose and clogged air filter, just as suggested. The repair was straightforward and cost 180 Euro total, including parts and labor. They did a complete intake system inspection, replaced the damaged vacuum hose, and installed a new air filter. The engine misfire codes cleared up immediately after the fix. Fuel economy is back to normal and that annoying hissing noise is completely gone. The check engine light hasnt returned either. Definitely learned my lesson about getting a proper diagnosis from a qualified shop rather than trying to save money at a general repair place. For anyone else facing similar symptoms, dont wait around hoping it will fix itself. A small vacuum hose issue can lead to bigger problems if left unchecked.