VW Phaeton Intake System Leak Causes Engine Misfire

Having dealt with a similar issue on my 2012 VW Passat diesel, I can share my experience. After noticing increased fuel consumption and the same hissing symptoms, my check engine light also came on persistently. The workshop performed leak detection tests around the intake manifold area and discovered a cracked intake hose. The turbocharger was actually fine, but the compromised hose was causing air to escape, leading to poor fuel economy and engine performance issues. The fix involved: Complete diagnostic scan, Pressure testing of the intake system, Replacement of the faulty intake hose, System check after repair Total cost was 100€ including parts and labor. The repair took about 2 hours and resolved all symptoms, the hissing disappeared, fuel economy returned to normal, and the check engine light cleared. To help more specifically with your Phaeton: What engine size do you have? Have you noticed any black smoke from exhaust? Does the hissing change with engine temperature? When was your last turbocharger inspection? This extra information would help identify if your issue matches what I experienced or might be something different.

Thank you for the detailed response. Just had my 80000km service last month where they replaced the air filter and did basic maintenance. The hissing sound is definitely most noticeable near the throttle body area, and the engine misfire occurs mainly during cold starts. I checked all visible vacuum hoses but found no obvious cracks. The black smoke only appears briefly when accelerating hard. The turbo was inspected during the last service and seemed fine according to the report. The engine is the 3.0L V6 diesel if that helps narrow down potential causes. Would it make sense to have the intake manifold pressure tested before replacing any parts?

Thanks for providing those details about your Phaeton. The symptoms you describe sound very similar to what I experienced, though my issue became more complex than initially thought. After my first diagnosis, we discovered the problem wasnt just the intake hose. The throttle body had carbon buildup causing irregular airflow, which contributed to the engine misfire during cold starts. The vacuum hose connecting to the intake manifold was also slightly degraded, creating a small leak that got worse under pressure. The complete fix required: Throttle body cleaning and recalibration, Vacuum hose replacement, Intake manifold pressure testing, Computer system reset Getting the intake manifold pressure tested is definitely the right next step. It helped identify the exact location of my leaks and prevented unnecessary parts replacement. The hissing near your throttle body strongly suggests this area needs inspection. With your engine size and mileage, its worth checking the seals around the turbocharger connection points as well. The brief black smoke during heavy acceleration could indicate a boost leak developing. The total repair in my case came to 350€, but catching it early prevented damage to other components.

I appreciate your informative response and experience with a similar issue. The suggestion about checking both the throttle body and vacuum hoses makes sense, especially since my symptoms match what you described. I just scheduled a pressure test focusing on the intake manifold area. Given that the hissing is most noticeable around the throttle body and the engine misfire happens during cold starts, your diagnosis seems spot on. Plus, the black smoke during acceleration hints at possible boost-related problems. One question though, did your repair also require any ECU reprogramming after the throttle body work? This would help me budget properly since 350€ seems reasonable if it includes all the suggested fixes. I will ask my workshop to specifically inspect the turbo connection points as well, since I want to address everything in one go. The systematic approach you took with testing before parts replacement is exactly what I was hoping to learn about. This gives me a clear path forward with my workshop rather than just throwing parts at the problem.