Mini Countryman engine concerns

That sounds similar to an issue I had with my Countryman. Reduced engine power and jerking, especially when accelerating, are familiar symptoms. I didn't notice any smoke, though. Have you checked the fuel octane you're using? Sometimes, lower octane fuel can cause engine knock, particularly in high-compression engines. It might also be worth checking the knock sensor; a faulty one can cause all sorts of problems. I wonder if it's worth investigating piston slap as well, although that's more of a lower-end noise, usually. It's just a thought though.

Interesting. When you say 'similar issue', are you suggesting it was carbon deposits? How did you diagnose it?

Yes, in my case, the garage determined it was excessive carbon buildup in the combustion chamber. They used a borescope to visually inspect the cylinder heads. Honestly, I'd recommend taking it to a trusted workshop. They can perform a proper diagnostic check and determine the root cause. It could save you time and money in the long run.

Thanks for the input. It was indeed excessive carbon deposits. Had the cylinder heads cleaned and the intake valves blasted. Runs like new now. Total cost was 425€.