Mini Cooper Engine Problem Resolved

I experienced similar symptoms with my Mini Cooper. A loud hissing sound during acceleration, coupled with the check engine light, suggests a vacuum leak. High fuel consumption further points to this issue. Please inspect the vacuum hose that connects to the intake manifold and throttle body. A crack or loose connection there is a likely culprit.

Thanks, that's helpful. Which specific vacuum hose did you have issues with? There seem to be a few connected to the intake manifold on my Mini Cooper. Any pointers on where to look first?

In my case, it was the vacuum hose connected directly to the intake manifold, near the throttle body. It had a hairline crack that was difficult to spot initially. If you're not comfortable diagnosing it yourself, a workshop should easily identify it with a smoke test.

Big thanks for the detailed info. Turns out it was indeed a cracked vacuum hose. Replaced it myself, got the part for around 100€. Check engine light is off, and the hissing is gone. Fuel consumption seems normal again. Appreciate the help!