Mini Cabrio engine behaving strangely

Sounds like your Mini's car computer is throwing a fit. A fault code with reduced engine power at that mileage often points to sensor issues or indeed, as you suspect, dodgy aftermarket tinkering. Did you run an auto scanner yourself, or did a garage give you the diagnostic code?

I used a generic auto scanner to read the diagnostic code. I'm not very familiar with car diagnostics myself. Is it possible the chip tuning is the direct cause, or could it be something else triggered by the tuning?

Think of it like this: the chip tuning rewrites the rules for your engine. If done poorly, it's like telling a chef to follow a recipe with incorrect measurements. The engine might be getting incorrect signals, causing all sorts of issues and throwing error codes. Given the symptoms and the tuning, it's highly probable that's your culprit. Best bet is to get it checked at a workshop; they should be able to confirm and rectify the issue.

As suspected, the issue was indeed related to a poorly implemented chip tuning. I had it removed and the car diagnostic was cleared. The dashboard light is now off, and the engine is performing optimally again. The overall cost was 180€.