RS4 Cold Start Issues Point to Failing Injector

I experienced a very similar fuel delivery issue with my 2008 S4. The symptoms were almost identical, rough idle and cold start problems that improved after warm-up. With some experience working on VAG engines, I recognized the classic signs of injector problems. My trusted workshop performed a comprehensive fuel system diagnostic. They used specialized equipment to test the injector spray patterns and discovered two faulty injectors that were causing inconsistent fuel delivery. The repair included: Complete fuel injection system inspection, Injector flow rate testing, Replacement of 2 defective injectors, Full system cleaning and calibration Total cost came to 515 Euro, but it completely resolved the rough idle and starting issues. The engine now runs smoothly from cold starts. To better assist with your case, could you share: Current mileage on your RS4? Check engine light status? Any recent fuel system maintenance? Are you noticing any unusual fuel consumption? Have you had the fuel pressure tested? This information would help determine if your symptoms match my experience with injector failure or point to other potential fuel system components.

Thanks for sharing your experience. My RS4 currently has 152591 KM and just had its annual service last month. After injector cleaning was performed at the last service, the hard starting problem persisted. The check engine light flashes briefly during the rough idle period but goes off once the engine stabilizes. Fuel consumption has increased by about 15% in the past month. No fuel pressure testing has been done yet. Based on your repair outcome, I will request a complete fuel system diagnostic, including injector flow testing, at my next workshop visit. The symptoms match closely with your experience, particularly the improvement after warm-up. Did your workshop mention how they determined which injectors needed replacement versus just cleaning?

Since my S4 repair, I learned a lot about diagnosing fuel injection problems. In my case, the workshop used specialized diagnostic equipment to measure the fuel rail pressure and individual injector spray patterns during cold start conditions. The testing revealed that cleaning alone wouldnt fix my faulty injectors because they had internal mechanical wear causing inconsistent fuel delivery. The technicians showed me the test results comparing the spray patterns, the bad injectors had very uneven distribution compared to the good ones. Your symptoms sound incredibly similar, especially the check engine light behavior during cold starts. The 15% increase in fuel consumption also matches what I experienced before the repair. This often happens when injectors arent atomizing fuel properly, leading to incomplete combustion. With your mileage being close to what mine was (I was at 148000 KM), injector wear is a common issue. Make sure your workshop: Tests fuel rail pressure during cold start, Performs individual injector flow rate measurements, Checks injector spray patterns while cold, Verifies the cold start enrichment function The comprehensive testing costs around 120 Euro but saves money by identifying exactly which components need replacement versus cleaning. Given how similar our cases are, I strongly suspect youll find at least one injector thats beyond just needing a cleaning service.

The symptoms match yours exactly, and your detailed feedback on the diagnostic process is really helpful. Since our vehicles have similar mileage and identical symptoms, I feel more confident about the likely cause now. I called my workshop and scheduled the complete fuel system diagnostic for next week. They confirmed they can perform all the test procedures you mentioned, especially the cold start spray pattern analysis and fuel rail pressure testing. Good point about checking the actual injector spray patterns rather than just assuming cleaning will fix it. The fact that my recent injector cleaning didnt resolve the rough idle issues suggests deeper mechanical wear, just like in your case. The 120 Euro diagnostic fee seems reasonable to pinpoint exactly which injectors need replacement versus cleaning. This should help avoid replacing parts unnecessarily. Will update once I get the test results and find out if worn injectors are indeed causing my fuel delivery problems. Thanks for the detailed comparison of symptoms and proper diagnostic steps. It helped confirm I am on the right track with suspecting injector failure rather than other fuel system components.