A4 Diesel Check Engine: Bad Air Valve Warning Signs

Having experienced similar symptoms with my A6 2.0 TDI (2013), this sounds like a vacuum leak affecting the air valve system. The check engine light and rough idle problems turned out to be caused by cracked vacuum hoses connecting the pump to the air valve. The repair required thorough diagnosis using smoke testing to locate the failing connection points. The main issue was a deteriorated rubber hose that had developed hairline cracks, allowing unmetered air into the system. These vacuum hoses tend to become brittle over time. This was a serious issue that needed immediate attention, as continuous running with vacuum leaks can affect other components and potentially damage the turbo system. The diagnostic process involved checking all vacuum lines, the air valve assembly, and ensuring proper sealing throughout the intake system. A competent shop should first perform a complete vacuum system inspection and verify the idle problems before replacing parts. The symptoms you describe, rough idling, power loss, and check engine warnings, align perfectly with vacuum system failures commonly seen in these engines. Request the shop to specifically inspect the vacuum hose connections and air valve assembly during diagnosis. Make sure they perform proper leak testing rather than just reading fault codes.

Thanks for sharing that detailed explanation. My issue turned out very similar, the manifold pressure was all over the place due to those vacuum leaks. It really helped having a proper diagnosis with the smoke test showing exactly where air was getting in. Quick question, do you remember the total repair cost for your case? Also curious if you had any other problems pop up after fixing the vacuum system and air valve? My shop mentioned these issues often come as part of a chain reaction, so would be good to know what to watch out for.

Had the repairs done last week actually and very happy with the outcome. The rough idle completely disappeared after they fixed the faulty hose connection from the pump to the air valve. Total cost was 175 Euro which included the diagnostic work and replacement parts. The vacuum leak testing identified the exact spots where the system was losing pressure. Since fixing the throttle body and air valve assembly, everything runs smoothly with no check engine warnings. The shop did a thorough job checking all vacuum hoses while they were at it, which gave peace of mind that no other issues were lurking. My advice would be to keep monitoring your engine performance over the next few weeks, but with a proper repair of the vacuum system, you shouldnt see related problems return. The key was finding a shop that took time to properly diagnose rather than just replacing parts out of nowhere.

The mechanic visit went better than expected. After reading up on vacuum leaks and air valve issues here, I knew exactly what to ask for during the inspection. The shop confirmed my suspicions using smoke testing, which showed multiple small leaks in the intake system affecting the manifold pressure. The fix involved replacing two cracked vacuum lines and cleaning the air valve assembly. Total cost came to 220 Euro including diagnostics, parts, and labor. Really glad I researched beforehand, helped avoid unnecessary parts replacement and kept costs reasonable. Been driving for about a week now. The idle problems are completely gone and no more check engine light. Engine runs much smoother, especially during cold starts. Just keeping an eye on things but seems like the repair addressed all the issues. Thanks again for the advice. Definitely saved me from another frustrating mechanic experience.