I';ve had that one to, it happens while braking. In my case, checking all the connections was the answer.
Try disconnecting everything->
then try to connect the throttle, try using it.
then disconnect it and try the cruise control, if you have one. maybe it will work on half speed
can you post the results of the above checkpoints?
after you checked your wiring harnas, also if you solderd this would be nice to know and if you could take picture of the wires, but that's only if the others don't succeed.