VW Transporter's Hissing Points to Air Intake Leak

Had similar issues with my VW Passat 2015 TSI. The symptoms match exactly what you describe, poor fuel economy, check engine light, and that characteristic hissing. The diagnosis revealed a split in the intake hose between the air filter housing and throttle body. The crack was allowing unmetered air to enter the system, causing the engine management to compensate by adjusting the fuel mixture. This explains both the increased fuel consumption and check engine warning. The repair involved replacing the intake hose assembly and performing a thorough inspection of the intake manifold and surrounding components. The technician also cleaned the throttle body while accessing the area, as carbon buildup is common in these engines. This is not typically a serious issue if addressed promptly, but running the engine with incorrect air-fuel mixtures for extended periods should be avoided. The repair was straightforward and took about 2 hours of labor. Would recommend getting it checked soon, as these symptoms rarely resolve themselves and can lead to running issues if left unattended.

Thanks for the detailed explanation, this matches my experience exactly. I also had a vacuum hose issue that caused an engine misfire and similar symptoms in my VW Transporter last year. The air intake system was the culprit, just as you described. Can you remember roughly what the repair cost in your case? Mine was fixed but I am curious to compare prices. Also, has everything been running smoothly since the repair or have you noticed any other issues with the air filter or intake system?

Since getting the repair done, everything has been running perfectly. The mechanic found and fixed the air intake system leak by replacing a cracked intake hose, which cost 100€ including labor. The fuel economy returned to normal immediately after the fix. Your experience with the vacuum hose matches what often happens with these engines. Regular inspection of the air filter and intake manifold components is important to catch these issues early. Been driving for about 6 months since the repair with no check engine lights or unusual sounds. The repair shop did a thorough job checking the entire intake system while they had it open. They noted the air filter was still in good condition, so no replacement was needed there. This kind of preventive inspection helped ensure there were no other developing issues.

Took my VW to a different mechanic after reading the responses here. Turned out it was exactly what was described, a cracked intake hose causing the air leak. The leak detection test confirmed it right away. Total repair came to 180€ including parts and labor, plus they cleaned the throttle body while they were at it. The engine misfire symptoms disappeared completely after the fix. Fuel economy is back to normal and that annoying hissing sound is gone. The mechanic showed me the damaged parts and explained how the intake manifold system works, which was helpful. Been driving for about two weeks now with no issues. The check engine light cleared up and everything is running smoothly. Really glad I got this sorted quickly before it could cause any bigger problems. Will definitely keep an eye on the air intake components during future services.