VW Lupo Stalling: Bad IAC Valve Needs Replacement

The symptoms you describe match what happened with my VW Polo TDI 1.9 (2003). The stalling engine and irregular idle speed were identical issues. The problem turned out to be a severely contaminated throttle body and air intake system. The idle control problems initially seemed like a faulty IAC valve, but thorough diagnostics revealed carbon buildup was restricting proper airflow. The throttle body needed complete cleaning and recalibration. This is a common issue on these diesel engines due to oil vapor recirculation. The fix required: Complete throttle body removal and cleaning, Air intake manifold decontamination, New gaskets, Electronic throttle adaptation, Clearing fault codes This was not a quick fix job, it required specialized cleaning equipment and programming tools. While not the most expensive repair, it needed professional attention due to the electronic adaptation requirements after cleaning. Most importantly, do not keep driving with these symptoms, as restricted airflow can cause additional engine damage over time. A proper cleaning should resolve both the stalling and check engine light issues.

Really glad you shared that info about the throttle body cleaning fix. My engine stalling problems sound exactly like what you dealt with. The IAC valve and idle control issues have been driving me crazy these past weeks. Did you remember roughly what the total repair cost was? Just trying to get an idea of what to budget for. Also curious if youve had any similar problems pop up since getting it sorted?

The repair actually cost me 425€ for the complete service. The mechanic confirmed it was indeed a bad idle air control valve combined with a heavily contaminated intake system, just as I suspected. The thorough cleaning and IAC valve replacement completely resolved the irregular idle problems. Since having the work done 8 months ago, the engine has been running smoothly with no stalling issues. The throttle body and air intake are working perfectly now, no check engine lights or idle control problems have returned. The key was addressing both the faulty valve and the buildup at the same time. The cost was worth it to prevent more expensive engine issues down the road. Make sure your mechanic does a complete intake system inspection when checking the IAC valve, as these issues often occur together in these engines.

Thanks for the detailed feedback about the throttle body cleaning. I took my Lupo to a new mechanic yesterday after reading about your similar experience. The diagnosis matched exactly what you described, contaminated throttle body and air intake causing the idle speed problems. Total bill came to 390€ which included cleaning, new gaskets, and recalibration. The mechanic showed me the carbon buildup they cleaned out, it was pretty shocking. The engine idle is now perfectly smooth and the check engine light is gone. Really relieved I got this sorted before it caused bigger issues. The IAC valve ended up being fine once they cleaned everything properly. Guess the first mechanic missed the real problem completely.