Q3 TFSI Engine Stalling Points to Faulty Air System

Having dealt with nearly identical symptoms on my 2013 Audi Q5 2.0 TFSI, I can relate to your situation. With some experience working on VAG engines, these symptoms often point to vacuum leak issues in the air intake system. My car showed similar behavior, unstable idle, occasional engine stalling at stops, and inconsistent manifold pressure readings. After checking with my workshop, they found a defective hose connection from the pump to the valve, which was causing air to leak. The entire diagnostic and repair process cost 175 Euro, including parts and labor. The throttle body response was noticeably smoother after the fix, and the engine stalling issues completely disappeared. The check engine light has stayed off since the repair. For a more accurate diagnosis of your Q3, could you share: Any specific error codes from your OBD readings, Whether the issues occur more frequently when the engine is cold or warm, If you notice any unusual sounds from the engine bay, Whether fuel consumption has increased This information would help determine if your issue matches what I experienced or if it might be something different in the air intake system.

My Q3 had its latest service just 2 months ago at 29364km and the workshop did a full inspection without finding any vacuum leaks. After reading about your experience, I checked my OBD reader again and got error code P0171 which suggests the system is running lean. The symptoms seem quite similar to what you described. The manifold pressure readings are indeed inconsistent and the throttle body response feels sluggish especially during cold starts. The air supply system might need a thorough check since the check engine light persists even after the recent service. The idle problems are definitely worse when the engine is cold. I can confirm there is a subtle whistling noise from the engine bay that wasnt there before. Could you share what specific tests your workshop ran to identify the faulty connection?

Thanks for the additional details about your Q3. The P0171 code combined with the whistling noise strongly suggests a vacuum leak, just like I experienced. My workshop performed a smoke test that quickly revealed the leak in the air supply system. The testing process involved: 1. A complete pressure test of the intake system 2. Smoke testing to pinpoint exact leak locations 3. Checking all vacuum lines and PCV system components The whistling noise you mentioned was identical to what I heard before my repair. The cold start idle problems and manifold pressure fluctuations are also textbook symptoms of an air leak affecting the fuel mixture. The total diagnostic process took about 2 hours. Given the similarities to my case, I suggest having them focus on: Vacuum lines connecting to the intake manifold, PCV valve and associated hoses, Intake manifold gaskets, All connection points in the air intake tract The check engine light should clear once the leak is fixed. In my case, the repair was straightforward once they found the exact location. Make sure they verify the fix with another smoke test to ensure no other leaks remain. Let me know how the diagnosis goes. The symptoms match my experience so closely that I suspect you will find a similar issue.

Thanks for sharing those test details. It helps knowing the smoke test was key in finding the vacuum leak source. I will definitely ask my workshop to run the same diagnostic steps, especially checking all the vacuum hoses and PCV system since the symptoms match yours perfectly. I took some more OBD readings this morning and the manifold pressure is fluctuating between 15-18 PSI at idle, which seems low. The whistling from the engine bay is most noticeable right after cold starts when the engine stalling also tends to happen. Given the P0171 code and air valve response issues, I agree it is likely an intake system problem. I will schedule the diagnostic tests this week and make sure they do a thorough smoke test. The 175 Euro repair cost you mentioned seems reasonable if they find a similar issue. Having the engine stalling at traffic lights fixed will be a huge relief. Thank you again for detailing your experience, it helped narrow down where to look for the problem.