Itsn't it true though Jason that when the tuner at Jabba put the basic map back into the car it would also show this same characteristic spiking it did with a more aggressive fuel map..........leaning towards the fact that something was coherently wrong with some part of the hardware.....and not the map.
Requested boost and what the n75 duty cycle were on par....its just that every time a certain amount of fuel was added the wild spiking would begin......many people on tdiclub have found this spiking to be so with and especially more so on the vnt2056's.....which is happy at around 1.6 bar but has soon has more fuel in introduced they over speed......and if too much is used down low at iq "let the surging biggin"
Try adjusting the actuator rod so its longer = slower spooling will accur but more controlerable boost will be possible when more fuel is added.....up to a point.
P.S........And i too know what its like when it doen't work out

.