Jetta TDI Rich Fuel Mix Causing Multiple Issues

Had very similar symptoms on my 2008 Golf TDI last season. The rough running and power loss turned out to be a faulty fuel injector. The rich mixture was causing black smoke and terrible fuel economy, just like your case. The diagnostic showed the injector was stuck partially open, flooding the cylinder with excess fuel. This requires complete injector removal and replacement, not a quick fix but essential to prevent further issues. If left unchecked, it can damage the catalytic converter from all the unburnt fuel. In my case, the air filter and intake manifold were also contaminated from the rich running condition and needed cleaning. The mechanic tested all injectors since they tend to wear at similar rates. Two were badly worn and got replaced. Common signs that confirm injector failure on TDIs: Rough idle and hesitation, Black exhaust smoke, Engine misfires during acceleration, Significantly worse fuel economy, Check engine light with injection-related codes This is definitely a job for a diesel specialist with proper diagnostic equipment. The injectors need precise calibration after replacement. Not something to attempt as DIY or trust to a general mechanic without TDI experience.

Thanks for sharing your experience. Our symptoms match almost exactly, especially the poor fuel economy and rough running. Getting this fixed soon sounds critical to avoid damaging the catalytic converter further. Do you remember roughly how much you paid for the injector replacement job? Also, have you had any other issues pop up since the repair was done? Just want to make sure I budget properly and cover all bases while its in the shop. The intake manifold cleaning you mentioned makes sense since all that excess fuel probably left deposits. Going to mention that to my mechanic when I take it in.

Thanks for asking about the follow-up results. The repair was completed last week and cost 515€ for replacing the defective fuel injector. The symptoms you described are now completely resolved, no more rough running or poor fuel economy issues. The mechanic confirmed the fuel injectors were causing the engine to run too rich, which matches exactly what you're experiencing. Getting this fixed promptly was crucial since excessive fuel can damage the catalytic converter over time. Since the repair, the engine runs smoothly with no hesitation during acceleration. The check engine light is off and fuel consumption has returned to normal levels. The intake manifold cleaning was included in the service to remove carbon deposits from the rich condition. No additional issues have emerged since the fix. The diagnostic testing showed the other injectors were still within spec, so only the faulty one needed replacement. Would definitely recommend having all injectors tested while the system is being serviced though, as they can wear unevenly. A proper diagnosis with specialized equipment is essential for these issues, as fuel injection problems often mimic other engine management faults.

Based on what everyone shared, I decided to take my Jetta to a diesel specialist yesterday. The diagnosis confirmed a faulty injector was causing the rich air-fuel ratio and rough running issues. They found excessive carbon buildup in the intake manifold from all the unburnt fuel. The oxygen sensor readings were way off due to the rich mixture. Total repair came to 780€ including parts and labor for replacing the bad injector, cleaning the intake, and running full diagnostics on the fuel system. The difference in how the car runs now is dramatic. No more jerking during acceleration, check engine light is off, and it feels like it has proper power again. The specialist explained that fixing it promptly likely prevented damage to the catalytic converter, which would have been much more expensive to replace. Really glad I asked here first and found a qualified shop instead of going back to my regular mechanic who might have missed the root cause. Money well spent to get it done right the first time.