Audi A8 EGR Issues Causing Multiple Engine Problems

Having dealt with nearly identical symptoms on my 2009 Audi A6 last year, this definitely sounds like a faulty EGR valve. As someone with moderate experience working on VAG engines, these symptoms match perfectly with what I encountered. The check engine light combined with rough idle and smoke strongly indicates an EGR system problem. My A6 displayed the same issues, particularly the power loss and that distinctive hissing noise under acceleration. The emissions test also failed before I got it fixed. The repair involved cleaning and ultimately replacing the EGR valve, which resolved all symptoms. Total cost was 355 Euro including parts and labor. The workshop confirmed that a stuck EGR valve can indeed damage your catalytic converter if not addressed promptly. To better assist, could you share: Current mileage? When was the last service done? Any fault codes being shown? Type of fuel you typically use? Whether symptoms get worse with engine temperature? Also worth checking for vacuum leaks, as these can sometimes mimic EGR valve symptoms. Getting this fixed sooner rather than later will prevent additional engine damage and restore proper performance.

Thanks for your input about the EGR valve symptoms. My A8 is currently at 129959 KM and had its last major service 6 months ago. I scanned for codes and got P0401 (insufficient EGR flow) along with a few others. The rough idle and vehicle emissions issues seem worse after the engine warms up. Running strictly premium fuel since day one, but the smoke and power loss started quite suddenly last week. Good point about checking vacuum leaks, I noticed the hissing gets louder when revving the engine. I will get it inspected soon to prevent any potential catalytic converter damage. The repair cost you mentioned seems reasonable if it fixes all these issues.

Thanks for the update. The P0401 code definitely confirms our EGR valve suspicions. When my A6 had this issue, I also noticed the symptoms worsening with engine temperature, exactly like yours. The hissing noise getting louder with revs strongly suggests a vacuum leak alongside the EGR problem. In my case, the vacuum lines near the EGR valve had deteriorated, contributing to the poor engine performance. The diesel engines in these cars are particularly sensitive to vacuum system integrity. While my repair initially focused on just the EGR valve, we ended up replacing several vacuum lines as well. The total came to about 425 Euro, slightly more than first quoted, but it completely resolved both the emissions test failures and performance issues. Given your mileage and the sudden onset of symptoms, Id recommend having both the EGR system and vacuum lines inspected. My mechanic showed me the carbon buildup in the old EGR valve, it was completely clogged, explaining the insufficient flow code youre seeing. Worth noting that after the repair, my fuel consumption returned to normal within two tanks, and the smoke completely disappeared. Let us know what the inspection reveals.

Thanks for all the detailed feedback. The codes and symptoms you described match my situation perfectly. I just scheduled an appointment for next week to have both the EGR system and vacuum lines checked. The automotive repair shop quoted me 450 Euro for a complete diagnosis, EGR valve replacement, and vacuum system inspection. After hearing about the potential recirculation issues and vacuum leaks causing these problems, I definitely want to get everything checked properly rather than just replacing parts blindly. Good to know the repair resolved your fuel consumption and smoke issues. The rapid decline in performance and increased emissions on my A8 have been concerning. I will update once I get the results from the inspection and repair work completed. Hopefully addressing these problems early will prevent any expensive catalytic converter damage down the line.