Saw this from another thread in the Turbo forum....
Originally Posted by bimmerpath
To those seeking to modify the flap in the exhaust - a warning. I had unplugged the wire harness behind the tail light panel to keep the flap open at all times. I performed this mod nearly a year ago. I had recently noticed a pulsing of the throttle at constant speed. The pulsing was getting progressively worse, to the point that I thought I was going to stall at some points. I took the car in, they ran all computer tests, couldn't find any faults, except for my disconnected harness mod. They didn't think that was a problem. They were stumped and began working with BMW engineers to find out what was causing the pulsing throttle. The cause- the disconnected harness was causing the computer to constantly calculate the correct parameters to compensate for the minor back pressure drops caused by the flap not closing (the flap should be closed at constant speed).
After all that, they loaded the new 30.0 software and cleared all adaptations.
As to the lag people are experiencing, it is my opinion that the drive-by-wire throttle adapts to peoples' driving habits and initially the throttle is not sure if you want full on gas, so it hesitates and then gives you the gas. Drive your car hard for a while and I think people will notice the responsiveness comes back - it has for me.
To all those who think the new software causes turbo lag, it would be nice if an engineer would chime in with their opinion. It would seem to me that turbo lag would be entirely mechanical and could not be effected by a software mod.