Revitalizing an old thread for an update... My sprint booster malfunctioned yesterday. It went full throttle when pulling away from the curb. Luckily there was only one car in front of me and I slammed on the brake and dodged it. Restarted the car a few times, tried turning the booster off, then green then red, but it still went to redline. Then my X5 went into limp mode and I drove back to my parking spot at about 2 mph (limp mode would only allow idle). I remove the booster and all is well. I hope it stays that way.