Beetle's Rough Idle Points to Exhaust System Damage

Had similar issues on my 2015 VW Golf GTI. The symptoms match what I experienced, rough idle, exhaust noise, and engine light. The oxygen sensor failed, which caused incorrect fuel mixture readings and triggered the check engine light. The faulty oxygen sensor made the engine run rich, leading to excessive fuel consumption and that strong exhaust smell. In my case, the sensor failure also damaged the catalytic converter because the engine ran too rich for too long. This required replacing both the oxygen sensor and catalytic converter to resolve the issues completely. The repair was significant since a damaged catalytic converter can cause major engine problems if left unchecked. Would recommend getting the error codes read first. Most oxygen sensor issues trigger specific codes that help pinpoint whether its the upstream or downstream sensor. The loud exhaust noise could indicate a leak at the sensor mounting point or a developing catalytic converter issue. Given the mileage on your Beetle and mention of recent work, have a reputable shop check the exhaust system thoroughly. Pay special attention to the oxygen sensor wiring and connections, as poor installation during previous work can damage these components.

Thanks for detailing your experience with the oxygen sensor and catalytic converter issues. Had very similar problems with my VW Beetle last winter. The engine light was flashing and the exhaust pipe noise got really bad. Found out the particulate filter was clogged and the EGR valve needed cleaning too. Do you remember roughly what you paid for the full repair? Curious if costs were similar. Also wondering if you had any other issues pop up since getting it fixed? Mine has been running fine but always good to know what to watch out for.

Thanks for asking about the repair outcome. After getting the exhaust treatment malfunction fixed at the shop, my GTI has been running perfectly with no check engine lights or performance issues. The Lambda sensor replacement cost 375€, which was actually less than expected given the symptoms. Unlike your situation, my particulate filter and EGR valve were fine, the malfunction was isolated to just the faulty oxygen sensor. The repair shop confirmed there were no exhaust leaks or other sensor problems like failing NOx sensors that often cause similar symptoms. Since the fix six months ago, fuel economy has improved and the exhaust smell is completely gone. The engine runs smooth even at idle now. Would suggest keeping an eye on your DEF fluid levels though, as sensor issues can sometimes mask other developing problems in the exhaust system. The key was catching it early before it could damage the catalytic converter like in my previous repair. Getting proper diagnostic work done by a certified shop really helped identify the exact issue rather than replacing multiple parts unnecessarily.

Wanted to update everyone on how this situation got resolved. Finally took my Beetle to a certified VW specialist after getting several opinions. The diagnostic scan showed both a failing oxygen sensor and a cracked exhaust pipe near the manifold, explains the awful smell and noise. Total repair came to 890€ including parts and labor. They replaced the oxygen sensor, fixed the exhaust leak, and did a thorough inspection of the catalytic converter which thankfully was still good. The exhaust pipe had apparently been damaged during that previous sketchy repair job when they didnt properly support the system while working on it. The car runs perfectly now, no more check engine light, rough idle is gone, and the exhaust noise completely disappeared. Fuel economy has improved too. Learned my lesson about using unqualified shops just to save money. The proper repair actually cost less than I expected given the symptoms. Really appreciate all the advice here that helped point me in the right direction. Having an idea what to look for definitely made me more confident dealing with the repair shop this time around.