S5 Diesel's Faulty Intake Manifold Causes Major Misfires

Recently dealt with similar symptoms on my A6 3.0 TDI (2020). The intake manifold issue started exactly like yours, rough idle, engine misfire during cold starts, and power loss. A vacuum leak in the manifold was causing unmetered air to enter, confusing the manifold sensor readings. The scorching around the gasket seals had created small cracks, leading to air intake problems. This is a serious issue that can damage engine components if left unrepaired. The repair required: Complete manifold removal, Replacement of damaged gaskets, Cleaning of carbon deposits, Testing all vacuum lines, Recalibration of sensors The manifold damage was extensive enough that it affected multiple cylinders. Car ran perfectly after the repair, with smooth idle and proper power delivery. This type of repair requires specialized diagnostic equipment and expertise with modern diesel engines. For reference, the symptoms worsened quickly over 2 weeks from first noticing the engine misfire to severe performance issues. Would recommend getting it checked immediately to prevent additional engine damage.

Thanks for sharing your experience. Those symptoms match what I went through with my S5 last winter. The manifold pressure issues and idle problems got really bad within days. Quick question, do you remember roughly what you paid for the complete fix? My repair bill was steep at around 2800 Euro including parts and labor, plus they found a cracked vacuum line while doing the work that added another 200 Euro. Has everything stayed running smooth since the repair? No other manifold sensor issues or engine performance problems popping up? Mine has been good except for a brief check engine light that turned out to be unrelated.

Happy to report my intake manifold repair has been completely solid since getting it fixed properly. The total came to 1180 Euro, which covered replacing the scorched manifold parts, new gaskets, and getting everything recalibrated correctly. That price was actually reasonable considering the detailed work needed on the manifold sensor system and the comprehensive testing they did. The engine performance has been perfect, no more misfires, rough idles, or manifold pressure problems. The repair shop did a thorough job checking all related components while they had it apart. Your 2800 Euro bill sounds high compared to my experience, though different shops and parts availability can affect pricing. After 8 months, I have not seen any check engine lights or noticed any power delivery issues. The stable manifold pressure readings confirm everything is working as designed. One key was having them do a complete manifold cleaning during the repair to prevent future gasket leaks.

Thanks for the input. I took my S5 to a different mechanic last week after researching recommendations. The experience was much better than my previous shop. They diagnosed a failing intake manifold and several damaged gaskets causing the air leaks. The engine misfire and rough idle were definitely from the vacuum issues they found. Total repair came to 2100 Euro including: New manifold assembly, Complete gasket replacement, Vacuum line repairs, Full system diagnostics, Carbon cleaning The check engine light cleared immediately after repair. Engine runs perfectly smooth now with proper power and no more exhaust smell. Idle is completely stable. The mechanic showed me the old damaged parts and explained everything clearly. Been driving it for a week with zero issues. Huge difference in performance compared to before. Glad I got it fixed before any serious engine damage occurred. The peace of mind was worth the cost.