I had that issue first time trying to do it too, the trick is to really stand on the brake pedal, you have to push it REALLY hard, untill you feel it touch the stop at the end of the pedal travel. When you open the throttle and the car is in launch you should not feel it straining or surging forward etc, it should just be like its revving in neutral. The car also doesn't hold at a constant RPM, but it revs between about 3000 and 3500. Also if you don't do it in the right order it doesn't work either, ie stop the car>TC off>sport>100% brake>100%throttle... if you only do say 85% brake, then try and do 100%brake it doesn't work. When it goes into launch mode you don't have to launch the car, you can just lift off the throttle to stop it.
There are a few videos on Youtube from Germany of it being done in Mk7 TDI's.
Cheers
Lewis
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