Audi S6 TDI Engine Misfires & Vacuum Leak Issues

I went through something very similar with my 2018 Audi A6 TDI. Have some experience with intake manifold issues after dealing with this problem last year. The symptoms you describe match exactly what I experienced, rough idle, engine misfire, reduced power, and that distinct exhaust smell. The vacuum leak from a scorched intake manifold was causing these issues. After the initial diagnosis, the mechanic found significant damage to the manifold, requiring a complete replacement. The repair took 3 days and cost 1180 Euro including parts and labor. The new intake manifold resolved all the symptoms completely, and the engine has been running smoothly since then. Early warning signs included: Slight power loss, especially during cold starts, Occasional rough idling before it became constant, Check engine light flashing intermittently, Unusual air intake sounds Could you share: Current mileage on your S6? When did you first notice the symptoms? Have you had any recent engine work done? Any diagnostic codes from the check engine light? This information would help determine if your situation is similar and whether you might be facing the same air intake system issues I encountered.

Thanks for sharing your experience. My car has 95489 KM and had its last service 4 months ago. The manifold sensor issues started about 2 weeks after the service. I noticed the engine becoming increasingly rough, though the vacuum leak symptoms developed quite suddenly last week. I got the car scanned and it showed P0299 and P0172 codes, pointing to air intake and fuel mixture problems. The dealership wants 1400 Euro for diagnostics and potential manifold gasket replacement, which seems steep. Based on your description, my car manifold might have similar damage. Would you recommend getting a second opinion from an independent shop, considering the quoted price?

Having gone through this repair on my A6 last year, I would definitely recommend getting a second opinion. Those error codes, P0299 and P0172, are exactly what my car showed before the intake manifold replacement was needed. The dealership price of 1400 Euro is notably higher than what I paid at an independent specialist. The manifold sensor and related components are accessible enough that any qualified shop with Audi experience can handle the repair. The timing of your symptoms, especially after a service, is interesting. My engine misfire issues also developed shortly after routine maintenance. This could indicate the air intake system might have been disturbed during the service, potentially causing or revealing an existing vacuum leak. The check engine light pattern and rough running are classic signs of manifold problems. In my case, waiting too long led to more extensive damage. Getting it fixed quickly prevented additional engine wear. A reputable independent shop should be able to diagnose this for around 100-150 Euro, with total repair costs likely closer to 1200 Euro if a full manifold replacement is needed. Make sure they use OEM parts though, aftermarket manifolds can cause recurring issues.

Thanks everyone for the detailed feedback. After getting a second opinion from an independent Audi specialist, I can confirm it was indeed the intake manifold causing the engine performance issues. The quote came in at 1250 Euro for full replacement including parts and labor. The manifold pressure problems were apparently made worse by a damaged gasket that started leaking after my recent service. The air intake system showed signs of wear that the mechanic said could have been caught earlier if I had investigated the initial rough running. The shop found the same error codes pointing to manifold sensor and vacuum issues. They recommended OEM parts to prevent future engine misfire problems. Scheduled the repair for next week since they had the parts in stock. Will post an update once the work is completed to share if it fully resolves the symptoms. Really appreciate all the insights shared here, helped me better understand the issue and make an informed decision on repairs rather than just accepting the higher dealer price.