lack of power between 2500 to 3000 rpms.now im thinking its a fuel problem.no check engine light.Changed coil,plugs,wires,by pass valve,fuel filter,new pedal thinking it was the plug on back going to throtle body,nope.sometimes i can step on gas an theres nothing just sputters,not the supercharger...fuel pump?i dont know,need help...2003 mini sjcw..

 

There is an ever so slight lag because there is a supercharger. It's less than that of a turbo but there is slight lag. Could need a tune?

 

I had similar issues on top of low end start power and it ended up being that little air line behind the supercharger intake, not sure if its one of the ones you quoted up top. I found it on YouTube and the guy actually found the problem solving on here lol, I hope this helps if that's the problem, it sure was for me. Still doing plugs and wire soon since we just got the car.

 

Is common issue at lot of R53 from 2003, can be solved with sw upgrade.