Yes, I know what you mean regarding being helpfull ! Sounds like you had a classic case of the turbo giving up and your spot on regarding what you call "runaway mode". They can end up burning there own oil as fuel and the car can rev so hard it will be knockinng like you don't know what, when this happens they have to be stalled to be stopped !
I would think as you drive yours it will settle down and should get better over the course of a few hundred miles, good luck and thanks for being so willing to share your experiances.
