I have 2003 R53, bought it from a dealer 2 months ago, for the most part the car is great. I do have a problem when accelerating past 10mph in first gear though. The throttle dips down for a second causing the car to lurch and then the car takes off as normal.

It feels just like if you were to quickly release the throttle and then depress it again just as quickly.

I have attempted to start off at different rpm's and the symptom is just the same, a dip in the throttle.

I don't believe it is the supercharger bypass valve as I have pressed on the spring and it is nice and stiff, as it should be. Anyway that causes a delay in the throttle which would occur in any gear at a specific RPM. This only occurs in first at exactly 10mph at any RPM. I have turned off ASC and it is still present.

I can get around it by shifting into second just before 9 mph and coasting through until 11mph before releasing the clutch but that is inconvenient and isn't really a solution.

I have done the ECU 'reset' using the trip buttons but that did not solve it either.

I believe it might be an ECU problem but I don't want to shell out the money for a new one if you guys have an better idea as to what it might be.

 

Not sure if this is your problem, but I did stumble upon this thread on NAM here about a similar hesitation in 1st. No real resolution given, but maybe you can post in there or PM the OP to see if he ever got it resolved.