VW Passat Hybrid Engine Stalling and Rough Idle Issues

As someone with some hands-on experience with hybrid systems, I dealt with a very similar issue on my 2017 VW Golf GTE Hybrid. The symptoms you describe match exactly what I experienced, particularly the check engine light and rough idle problems. After inspection, my workshop found that the vacuum hoses connecting the pump to the air valve were deteriorating, causing inconsistent air intake flow. This explained both the stalling and rough idle problems you mentioned. The repair involved replacing the defective hose connections and performing a thorough check of the entire air intake system. The total repair cost was 175€ and took about 2 hours to complete. Since the fix, the idle problems disappeared completely and the check engine light has not returned. However, to provide more specific guidance for your case, could you share: Have you noticed any unusual sounds from the engine bay? Does the problem occur more frequently in specific weather conditions? What error codes is the check engine light showing? When was your last scheduled maintenance? These details would help determine if your issue is identical to what I experienced or if there might be other factors involved with the air intake system.

Thanks for sharing your experience. My latest service was just completed 2 weeks ago at 106706km and the technician found no obvious vacuum leaks or intake issues during inspection. The engine stalling happens mostly during cold starts, and I hear a distinct hissing sound from the engine bay when this occurs. The check engine light shows a P0171 code which points to a lean fuel mixture. The manifold pressure readings are inconsistent according to my OBD scanner. I checked vacuum hoses visually but found no obvious cracks. Would it make sense to have a smoke test done to check for less visible vacuum leaks before replacing parts? Want to be certain before spending money on new components.

Great that you got the code read, P0171 points directly to a lean condition, which aligns with my previous experience. Even though no obvious vacuum leaks were found, the inconsistent manifold pressure readings from your OBD scanner strongly suggest a vacuum system issue, just like what I encountered. A smoke test is absolutely worth doing, I actually skipped this step initially and ended up replacing parts unnecessarily. The small hairline cracks in my vacuum hoses were not visible during a basic inspection, but the smoke test would have revealed them immediately. These tiny leaks were enough to create problematic air intake readings and trigger idle problems. The hissing sound you describe matches exactly what I heard before my repair, it was most noticeable during cold starts when the engine was trying to maintain proper idle. The manifold pressure variations occurred because the system was pulling in unmetered air through those barely visible vacuum hose defects. The smoke test typically costs around 80€ and could save you from replacing unneeded parts. My recommendation based on this identical issue in my hybrid would be: 1. Get the smoke test done 2. Have all vacuum hoses inspected under pressure 3. Check the air intake boots for any splits 4. Verify manifold pressure sensor readings after repairs

I appreciate the detailed response. The smoke test seems like the logical next step before jumping into parts replacement. The symptoms you described with your hybrid match my situation perfectly, especially the connection between the manifold pressure variations and the hissing sound during cold starts. I will schedule the smoke test this week to properly diagnose these air supply issues. The 80€ diagnostic fee makes sense if it prevents unnecessary parts replacement. Given that my idle problems and air intake concerns match your experience so closely, I am hopeful this approach will identify the root cause. Will monitor the manifold pressure readings on my OBD scanner in the meantime. The inconsistent values during idle definitely suggest vacuum leaks somewhere in the system. Thanks for helping me avoid the trial-and-error parts replacement you initially went through. Will update once I get the smoke test results back.