S60 Hissing and Fuel Consumption

Had similar symptoms on my old Vauxhall Astra. Turned out to be a split in a vacuum hose going to the turbocharger. Is the hissing sound constant, or only when the turbo is engaged?

The hissing intensifies under load, especially when the turbo spools up. Does that point to a compromised intake hose? What happened to your fuel economy when this happened? Trying to understand how bad it is.

Sounds like the same issue. My fuel economy went down noticeably. I'd suggest getting it checked at a workshop; they can pressure test the system to find the leak.

Took it to a mechanic and it was a cracked intake hose. Replacement cost 100€ including labor. The hissing is gone, the check engine light is off, and my fuel economy is back to normal. Thanks!