Mercedes B Klasse Hybrid EGR Valve Issue

Whoa, that's quite the laundry list of problems! A defective EGR valve is definitely a prime suspect given those symptoms on your hybrid. The hissing sound is interesting though; are you certain it's not a vacuum leak somewhere else in the system? Sometimes those can be tricky to pinpoint and can mimic EGR valve issues. Does the hissing get worse with engine RPM, or is it constant?

The hissing intensifies with RPM, during acceleration. I considered a separate vacuum leak, but the symptoms pointed to the EGR valve. Is there a way to isolate the hissing source and verify if it's the EGR valve or something else?

Okay, if the hissing is tied to RPMs, it really could be a vacuum leak related to the EGR. Honestly, with all the symptoms you're describing, and especially given the mileage on your model, I'd strongly advise taking it to a trusted workshop. They'll have the diagnostic tools to properly test the EGR valve and the vacuum system. Messing with the EGR on a hybrid can be tricky and you might make things worse, or even damage vehicle emissions systems.

I appreciate your candid advice. Given the complexities of the hybrid system and the potential for unintended consequences, I've decided to heed your recommendation and seek professional assistance. The estimated automotive repair cost of 355€ seems reasonable enough for an EGR valve replacement, especially considering the potential for further complications if I were to attempt a repair myself. Thank you again for your time and expertise.