S4 Idle Control Issues Point to Failed IAC Valve

As someone with moderate experience working on cars, I had a very similar issue with my 2013 Audi S5. The symptoms you describe match exactly what I experienced, engine stalling at idle and inconsistent idle speed control. Initially, I also thought it was the IAC valve, but when I took it to the workshop, they diagnosed a heavily contaminated throttle body. The carbon buildup was causing irregular idle speed and stalling. The complete cleaning service, including labor and parts, cost me 425 Euro. The fix completely resolved my engine stalling issues. The idle speed returned to normal, and the check engine light disappeared after they cleared the codes. Before suggesting specific solutions for your case, it would help to know: Current mileage on your S4, When was the last time you had a throttle body service, Are there any other symptoms besides the stalling engine, What specific error code is showing up on the scanner The throttle body contamination is fairly common on these engines, especially if regular maintenance has been delayed. The symptoms can mimic IAC valve issues, which is why proper diagnosis is important.

Last service was done at 87302 KM, and the error code shows P0505. After cleaning the throttle body and air valve, the stalling persisted. The mechanic suggested a complete idle control valve replacement since the cleaning didnt fix the engine stalling. The part itself costs around 380 Euro plus labor. Would like to get a second opinion before proceeding with such an expensive repair, especially since the idle control issues continue even after the thorough throttle body cleaning. Has anyone found a more cost-effective solution for this specific issue? The engine stalling mainly occurs during warm idle conditions, which makes me question if the IAC replacement is really necessary.

I completely understand your hesitation about the IAC valve replacement cost. After my initial throttle body cleaning on my S5 didn't resolve the stalling engine issue, I also faced a similar dilemma. In my case, I did end up replacing the IAC valve because the engine stalling persisted after cleaning. The P0505 code specifically points to the idle control system, and given that cleaning didn't help, replacement was indeed necessary. The 380 Euro price for the part is actually standard for these models. My total repair cost including labor came to around 650 Euro. While expensive, it completely resolved the idle speed problems and the engine stalling issues haven't returned in over 50000km. Before you proceed, consider having them check: Vacuum lines for any leaks, MAF sensor condition, Carbon buildup in the intake manifold However, given the error code and the fact that cleaning didn't help, replacing the IAC valve is likely the correct solution. The warm idle stalling symptom is particularly indicative of a failing idle air control valve rather than other potential causes.

Thanks for sharing your experience. The error code P0505 combined with the persistent engine stalling after cleaning does point toward the IAC valve being the culprit. While 380 Euro for the part seems steep, it makes sense given my symptoms havent improved after the throttle body service. I will schedule the IAC valve replacement next week. Hopefully this resolves the idle control issues completely. Will definitely check those vacuum lines and MAF sensor too since the engine has significant mileage on it. Better to address all potential issues while the car is in the shop rather than having to deal with more engine stalling problems later. Really helpful to hear that your idle speed problems were fully resolved after replacing the air valve. At least I can feel more confident about spending the money knowing it fixed the same issues in your case. Will update once the repair is complete to confirm if it solved my stalling engine problems as well.