I'm concerned about carbon build up on my 2016 Mazda CX-5, 48k miles.
When I read about how to fight the ill effects of direct injection, I read - use top tier gas, keep OCI to 5k miles, use (a specific) sythetic oil with a low sodium level, use a catch can, catch cans don't help, use valve cleaner additives, valve cleaner additives are no help, rev the car into the red line weekly, and finally...walnut blasting is your only hope to alleviate the problem.
I don't think that anyone knows for sure what to do.