Hi there,
Never worked out what caused mine to do it to be honest.
Sold the car a number of months after I made this post, I figured however that either the injectors could keep up with the fuelling or it was a breathing fault.
I figured as I was never going to go that speed again I'd not worry about it.
The best way is to find someone local with VAGCOM ask them to hook it up. it should of brought up a fault.