Hissing Audi A4: EGR Valve Issues and Black Smoke

Had a similar issue with my 2008 Audi A3 last spring. The symptoms you describe match exactly what I experienced, rough idle, increased fuel consumption, and that distinctive hissing noise that would make the engine feel underpowered. After failing an emissions test twice, I took it to a workshop. They diagnosed a completely jammed EGR valve. Cleaning wasnt an option in my case since it was too far gone. Total repair cost was 355 Euro including parts and labor. The improvement was noticeable immediately after the repair: Smooth idle restored, Normal fuel consumption, No more black smoke, Check engine light cleared, Engine power back to normal To prevent future issues, regular maintenance is key. The workshop advised running the engine at higher RPMs occasionally to help prevent carbon buildup. Could you share: Current mileage on your A4? When was the last time you had a major service? Have you scanned for error codes? Does the problem get worse when the engine is warm or cold? This information would help determine if your symptoms indeed point to the EGR valve or possibly a vacuum leak somewhere else in the system.

Thanks for the detailed suggestions. My A4 had its last major service at 125000 KM, about 2000 KM ago. The mechanic pulled error codes showing a potential vacuum leak and high emissions readings through the catalytic converter. The symptoms definitely worsen when the engine is warm, particularly after highway driving. I will try running it at higher RPMs as suggested. The check engine light has been persistent since these issues started. Looks like I might need to budget for that 355 Euro repair cost you mentioned, though hoping a thorough cleaning might work first.

Based on those error codes and symptoms, especially the worsening after highway driving, I'm even more convinced its the EGR valve. On my A3, the high emissions readings through the catalytic converter were also present before the repair. A vacuum leak test confirmed the EGR valve was the culprit rather than a general vacuum leak. The rough idle and vehicle emissions issues cleared up completely after replacement. If youre experiencing similar progression of symptoms, starting with minor power loss and developing into more serious performance issues, its a classic EGR valve failure pattern. While cleaning might work temporarily, in my experience with these engines, once you see multiple symptoms (rough idle, smoke, and performance issues), a full replacement is usually needed. The carbon buildup typically damages the valve mechanism beyond restoration. Since youre only 2000 KM past your last service, its worth noting that EGR problems can develop quite suddenly, especially if there was existing carbon buildup. The check engine light staying on with confirmed high emissions points strongly to this being more than just a need for cleaning. Keep monitoring your fuel consumption, on my A3, it returned to normal within the first tank after repair. Worth having the vacuum system thoroughly checked while they do the work to rule out any other leaks.

Thanks for the input. After reading about similar experiences, particularly regarding the vacuum leak test results, I feel more confident about tackling this repair. The error codes showing high emissions through the catalytic converter combined with the check engine light and performance issues seem to clearly point to EGR valve failure. I checked with a local shop and got quoted 340 Euro for a complete replacement. Given the similarities to other cases where cleaning didnt provide a long-term fix, I will go ahead with the full replacement rather than just attempting a cleaning. The consistent warm-engine symptoms and high fuel consumption are too similar to ignore. Will schedule the repair next week and make sure they check the entire vacuum system while theyre at it. Really hoping to see the same immediate improvements in performance and fuel economy that others reported. Will definitely follow the advice about running at higher RPMs occasionally to prevent future carbon buildup. If anyone needs an update after the repair, let me know how it worked out. These vehicle emissions issues and check engine warnings need to be addressed properly to avoid bigger problems down the line.