Audi S4: Rough Idle and Fuel System Woes Fixed

Had a similar situation with my 2005 Audi S6. As someone with moderate experience working on cars, I initially thought it was just a fuel injector issue, but the symptoms you describe match exactly what I encountered, engine misfire, rough running, and stalling problems. After some troubleshooting, my workshop found it was actually a loose wiring connection to the fuel pressure sensor. The connection had corroded over time, causing inconsistent readings and making the engine run poorly. The total repair cost was 95 Euro, which covered cleaning the connections and securing the wiring properly. The fuel economy improved significantly after the fix, and all the running issues disappeared. The engine stalling problems that were particularly annoying at traffic stops were completely resolved. Before suggesting more specific solutions, could you share: Have you noticed any specific patterns when the stalling occurs? What fuel type are you using? Has the fuel filter been replaced recently? Are there any specific error codes showing? This information would help determine if youre dealing with the same root cause or if its potentially a different fuel system issue.

Last service at 93013KM. After reading your experience, I checked the error codes using an OBD scanner. Getting P0190 and P0087 codes which point toward fuel pressure problems. The stalling mainly happens when stopping at low speeds. I use premium 98 octane fuel, and the fuel filter was replaced during the last service. The rough idle gets worse when the engine is warm, and fuel delivery seems inconsistent. The fuel economy has dropped about 25% in the last month. Based on your feedback, I will have the wiring connections inspected, as this seems like a cost-effective first step before replacing any parts. Since posting my initial question, I also noticed a slight fuel smell, which might indicate a leak somewhere in the system. This could explain the engine misfire and poor performance issues.

Responding to your latest update, the fuel smell you mentioned is concerning and definitely changes the diagnosis path. With my S6, I didnt have any fuel odors, which is why the wiring fix alone solved my issues. The P0190 and P0087 codes combined with a fuel smell suggest you might be dealing with a fuel pressure issue AND a potential leak. The fuel pump assembly might need attention, as these units often develop leaks around the seals when they start failing. In my case, examining the wiring was the right first step, but your situation sounds more complex. The rough idle getting worse with a warm engine and the 25% drop in fuel economy matches classic symptoms of a failing fuel pump. The pump might be struggling to maintain proper pressure when hot, leading to the engine misfire and performance issues. Given these symptoms, I recommend: 1. First locate the source of the fuel smell for safety 2. Have the fuel pressure tested with a gauge 3. Check the entire fuel pump assembly A complete fuel pump replacement on these models typically runs 400-600 Euro including labor. My initial wiring fix was much cheaper, but based on your additional symptoms, you might need more extensive repairs to resolve all issues.

Thanks for sharing the detailed information about your experience with your S6. Those error codes (P0190 and P0087) definitely match what I was seeing with my fuel system problems. The fuel smell I mentioned has actually gotten a bit stronger over the past few days, especially after the car sits for a while. I took your advice and had a mechanic perform a pressure test yesterday. The readings were inconsistent and well below spec, confirming the fuel delivery problems. They also found a small leak at the fuel pump assembly seal, which explains the fuel odor. Given the age of the car and the multiple symptoms, I decided to go ahead with a complete fuel pump replacement rather than just trying to fix the wiring. The parts and labor quote came to 550 Euro, which seems fair based on the price range you mentioned. The car goes in for repairs next week. Really appreciate the guidance, it helped me make a more informed decision about the repair approach instead of just throwing parts at the problem. Will update once everything is fixed.