Verso Hissing Noise Power Loss

That sounds familiar. My 2016 Opel Insignia had similar issues: hissing, power loss, and the check engine light. Does the engine power go up and down, or is it just always weak?

The power seems to change, especially when the air temperature changes a lot. Does that make it even more likely it's the air sensor itself?

Yes, that makes a faulty sensor or connection even more likely. Given the error code and power changes, checking the wiring is a good start. Honestly, I'd suggest a workshop look at it. It could save you time and problems.

I took your advice and had it checked. It was the cable for the charge air temperature sensor. The repair was 95€. Thanks for the help!