When the car falters, do you get any check engine lights?  If so, can you get the codes so we can get some direction as to what the computer is seeing?

I presume the car runs 'normal' until it falters - good acceleration and smooth idle?

Bypass valve can be the culprit, but I would suspect you wouldn't have strong acceleration under 4k rpm....

You should be able to detect any vacuum leaks with a smoke test...

I have a 2002 R53 with about a hundred 22000 miles on it recently in the last couple of weeks at 4000 RPM he just Falls flat on his face. Getting on the freeway is very dangerous. Been reading some different stuff and a lot of things point to the bypass valve, possibly the supercharger boots? II just need some some  Insight