there have a been a few threads about this, and it seems to be the newest software and how it primes the hpfp (possibly) prior to starting. I too was getting rough starts but after a minute of idling, no codes or anything and then the car ran completely fine.
Although, after I complained about it to my dealer (it took 2 times...) they replaced the hpfp and the car starts right up now. It is always something with the n54
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