Well good luck with a BM in a Honda garage...I doubt they will even know where to start. And as to which part you think they are going to swap
If a BM dealer fitted a new airbox and ICV then there are lots of pipes and stuff, the secondary air supply system etc. etc. and the set up of the ICV. I would have had it back to the dealer within minutes of the first problem and tell em to get it right. If the Honda dealer touches it then BM won't be too happy at having it back as 'someone else has been fiddling with it'.
Dieseling, or running-on is a pain and the causes can be numerous but a hot-spot in the combustion chamber is the most likely culprit and this is most commonly caused by the plugs. If you want to terrify yourself take a look here...
https://www.howacarworks.com/illustrations/causes-of-running-on...or here...
https://axleaddict.com/auto-repair/Why-My-Engine-Keeps-RunningWrong plugs can be a cause, (s'funny that they have just changed them) as can fuelling issues (s'funny they have just had the airbox and ICV out).
Get the BMW dealer to collect it and fix it. I can almost guarantee that it is their work that is causing it.