Mercedes B Klasse Hybrid check engine light and air valve issue

Whoa, that sounds familiar! I had a similar problem with my old Fiat, though it wasn't a hybrid. The symptoms sound like a classic vacuum leak to me. Check your vacuum hoses, especially around the air intake. When those hoses get old, they can crack and cause all sorts of mayhem, like engine stalling or rough idling. It's worth a look!

Interesting! When you say 'vacuum hoses', are we talking about the little rubber hoses connected to the air valve and the pump? Are there any specific areas I should focus on? I'm a bit of a novice when it comes to this stuff, so any pointers would be greatly appreciated!

Yep, those little rubber vacuum hoses are exactly what I meant! On my Fiat, the problem was a tiny split in one of the hoses near the air intake manifold. It was causing a major vacuum leak, which messed with the air-fuel mixture. Honestly, unless you're super confident, I'd suggest taking it to a workshop. They can do a smoke test to find any vacuum leaks super fast.

Thank you so much for the advice! I took it to a workshop, and you were spot on! It was indeed a defective hose connection from the pump to the air valve causing a vacuum leak. Repair cost was 175€. Problem solved!