emma_shadow7
Audi S4 Power Loss and Stalling: MAF Sensor Alert
Loss of engine power
Stalling while idling
Jerking on acceleration
Shaking while idling
Check engine light on
4 comment(s)
Thanks for the replies. My last service was 2 months ago at 32166 KM. The scan shows P0171 code which points to a lean air-fuel ratio condition. The oxygen sensor readings are erratic according to the diagnostic report. After checking further, there is also a slight whistling noise near the throttle body area which might indicate a vacuum leak. The catalytic converter was replaced during the last service, so I doubt that would be the issue. The mass airflow sensor might need cleaning or replacement since these symptoms started appearing more frequently during cold starts.
Thanks for the additional details, this actually sounds quite different from my S5's injector issue, especially with that P0171 code and the whistling noise you mentioned. The lean air-fuel ratio combined with the symptoms you describe strongly suggests a vacuum leak, which matches my experience with vacuum-related issues. When my car had similar symptoms, I first cleaned the throttle body and mass airflow sensor, but this only provided temporary relief. The real culprit turned out to be a cracked vacuum line near the intake manifold. The rich mixture warning kept appearing until we found and fixed that leak. The repair process involved: Smoke testing to locate the vacuum leak (85 Euro), Replacing the damaged vacuum line (120 Euro), Cleaning the throttle body and mass airflow sensor (95 Euro), Basic diagnostic reset and testing (65 Euro) Total cost came to about 365 Euro, significantly less than replacing major components. After the repair, both the check engine light and performance issues disappeared completely. Since your symptoms are worse during cold starts and you have that distinct whistling noise, I strongly recommend having the vacuum system smoke-tested before replacing any expensive components like the mass airflow sensor.
Thanks everyone for the helpful input. Based on the whistling noise and the P0171 code pointing to a lean air-fuel ratio condition, I am going to have the shop do a smoke test first to check for vacuum leaks. Makes sense that the erratic oxygen sensor readings could be caused by unmetered air entering through a vacuum leak rather than a faulty mass airflow sensor. I will schedule the diagnostic testing tomorrow and request they start with checking all vacuum lines around the intake manifold area. The total estimate of 365 Euro for similar repairs seems reasonable compared to replacing major components. The check engine light symptoms definitely align with a vacuum system issue rather than my initial suspicion of fuel delivery problems. Will update once I get the smoke test results and confirm whether its just a simple vacuum line that needs replacing. Really appreciate all the detailed responses that helped narrow down the likely cause.
I had a very similar issue with my 2015 Audi S5, and as someone with moderate experience working on cars, I can relate to your situation. The symptoms you describe match exactly what I experienced, the check engine light, power loss, and rough idling were all present in my case. After initial diagnosis, my mechanic found that one of the fuel injection valves was faulty, causing improper fuel delivery. The defective injector was disrupting the fuel-air mixture, which explains the performance issues. The repair included replacing the faulty injector and testing the fuel injection system thoroughly. The total cost came to 515 Euro, including parts and labor. The mass airflow sensor and intake manifold were initially suspected, but diagnostic testing confirmed it was specifically the injector causing the problems. Since getting it fixed, the car has been running smoothly with no recurring issues. Before offering more specific advice, could you provide: Current mileage on your S4, Any recent maintenance history, Whether you notice these issues more during cold starts or when the engine is warm, If there are any specific error codes from the check engine light This information would help determine if your case is similar and if you might be dealing with the same injector issue.