Audi S1 Fuel Regulator Issues Causing Engine Trouble

I had a similar issue with my Audi S3 (2016) and have some experience with fuel system troubleshooting. The symptoms you describe match what I encountered, poor idle, reduced power, and an active check engine light. After changing the fuel filter, I got an error code related to the fuel pressure. The workshop diagnosed the issue using pressure testing on the fuel rail and found that the fuel regulator was indeed malfunctioning. They also checked the fuel pump performance as these components work together in the fuel delivery system. The repair was straightforward, replacing the regulator resolved all symptoms. Total cost was 45 Euro for the diagnostic and repair work. The fuel efficiency improved significantly after the fix. To provide more specific advice for your S1, could you share: Current mileage, Any modifications to the fuel system, Recent maintenance history, Specific error codes if you have them, Whether the issues started suddenly or developed gradually This information would help determine if your case matches what I experienced or if other components might need inspection.

Just had my last service at 161630 KM. Thanks for the detailed response. After your mention of error codes, I checked with my OBD reader and got P0087 which points to fuel rail pressure too low. The engine misfire happens mostly when the engine is cold, and the rough idle gets worse when the AC is on. No modifications to the fuel system, all stock. The problems started gradually over the last month. Going to schedule a pressure test based on your experience, seems like the fuel regulator is indeed the likely cause.

Thanks for providing those details. The P0087 code matches exactly what I encountered with my S3, it definitely strengthens the fuel pressure regulator theory. When my issues occurred, I also noticed the same cold-start misfires and AC-related idle problems. The fuel pressure test is the right next step. In my case, it showed the fuel rail pressure dropping below spec when the fuel regulator failed to maintain consistent pressure. The workshop also confirmed that the fuel pump was still delivering adequate flow, ruling out a pump failure. Since your mileage is similar to what mine was when the issue occurred (around 155000 km), and the symptoms developed gradually just like mine, I suspect you're dealing with the same component wear. The regulator tends to deteriorate over time, leading to inconsistent fuel delivery. Quick tip from my experience: have them inspect the fuel rail and lines while testing the pressure. In my case, they found some debris in the fuel rail that could have contributed to the regulator failure. A thorough cleaning of the system during the repair helped prevent any recurring issues.

The P0087 code definitely confirms what I was suspecting with the fuel rail pressure. I appreciate the insight about checking for debris during the pressure test, will make sure to mention this to the workshop. Your experience with similar mileage and symptoms gives me confidence about the diagnosis path. Knowing the AC connection to the rough idle and the cold start issues are common with fuel pressure problems helps a lot. Will get it booked in for the pressure test and regulator replacement. The fuel efficiency impact you mentioned makes sense given how the engine has been running. Based on your timeline, better to get this sorted soon before it potentially affects other fuel system components. I will make sure they do a thorough inspection of the fuel pump and lines while they are at it. Thanks for the detailed troubleshooting help, saved me some diagnostic time with the workshop.