SQ7 Diesel Stalls: IAC Valve Causing Cold Start Issues

Had similar symptoms with my 2019 A6 3.0 TDI. The engine stalling during idle was caused by heavy carbon deposits in the air intake and throttle body. Initially thought it was just the idle control valve, but inspection revealed extensive contamination throughout the intake system. The main signs matched yours, unstable idle, especially during warm-up, and engine stalling. The check engine light kept coming on due to irregular air-fuel mixture readings. Required a complete intake system cleaning, including throttle body cleaning and decarbonizing treatment. The idle control valve also needed replacement as the contamination had damaged its internal components. This was a serious repair job taking about 6-7 hours of labor. The car runs perfectly now with smooth idle. Would strongly recommend getting it checked soon, as continued operation with a contaminated intake system can lead to more expensive damage to engine components. These symptoms typically show up in diesel engines around your mileage range. Consider a preventive intake cleaning every 60000km to avoid this issue in the future. The stalling will likely get worse if left unaddressed.

Thanks for the detailed reply on the SQ7 stalling issue. The symptoms you described with the air intake and throttle body contamination match my situation perfectly. Car runs much better after warm up, but the engine stalling during cold starts is becoming a real hassle. How much did the complete repair job end up costing you? Also curious if youve had any similar issues pop up since the cleaning and air valve replacement? Planning to book mine in soon and want to budget accordingly.

Thanks for asking about the costs. After taking it to the mechanic last month, the diagnosis confirmed what I suspected, a bad idle air control valve combined with heavily contaminated intake components. The total repair came to 425 Euro, which included a thorough cleaning of the entire intake system and IAC valve replacement. Since the repair, the engine idles perfectly and the stalling issues have completely disappeared. The throttle body response is much smoother now, especially during cold starts. No check engine lights or idle speed problems have returned in the past 4 weeks of daily driving. The mechanic mentioned that the level of contamination they found was pretty typical for a diesel at this mileage. The idle control system just cant function properly when theres that much carbon buildup. Definitely worth getting it sorted before it leads to more serious engine issues.

Had my car fixed last week after getting your advice. The mechanic found exactly what you described, heavy carbon deposits in the intake system and a faulty IAC valve. Total bill came to 580 Euro, bit more than yours but included some extra diagnostic work. The difference in how the engine runs now is remarkable. No more stalling during warm-up and the idle speed stays perfectly steady. The throttle body cleaning made a huge difference to the overall engine response. Check engine light has stayed off since the repair. They showed me the old parts and the carbon buildup was shocking. Guess this is pretty common on these engines at high mileage. The mechanic recommended regular intake cleaning every 60000km to prevent future idle control issues. Money well spent considering how much better the car runs now. Will definitely keep up with the maintenance schedule to avoid dealing with engine stalling issues again. Thanks for steering me in the right direction with the diagnosis.