The CPO 335d I just purchased, I noticed the intake manifold was replaced by the dealer, along with the fuel injectors right before they advertised it for sale. Carbon build up is definitely an issue in these cars. I did not let this discourage me from buying the 335d.
They updated the car to the latest software, parts, etc. Let's see if the problem comes again. I have 100k warranty, so not concerned yet.
Back to the question, does tune(s) have any correlation with carbon build up...