Trafic Hissing Noise and Fuel Consumption

Hissing under acceleration and higher fuel consumption with a check engine light on a Trafic? Classic symptoms. Air intake leak is a reasonable start. Have you checked all the intake hoses between the air filter box and the turbocharger? Any sign of cracks or splits? What codes are you pulling from the check engine light, and did you inspect the air filter?

Codes? Haven't pulled any codes yet. Should I definitely do that first? And you mentioned the turbocharger hoses... are they a common culprit? Is there a method to detect the leak, because I visually inspected the hoses and didn't see any obvious issue?

Yes, get the codes read. It will point you in the right direction. If you can't see any splits in the intake hoses, you can try listening closely around the joints with the engine running. Or carefully use soapy water to detect bubbles around the intake. Turbo hoses are common, especially with age. Though I'd suggest going to a trusted workshop; intake leaks can cause misfires. Save yourself a headache.

Thanks! It was a split intake hose after the air filter, just like you suspected! Replaced it, cleared the code, and she's running sweet again. Cost me around 100€ for the hose and a bit of elbow grease. Check engine light is gone, fuel economy is back to normal, and the hissing is history!