Right, so I went over and had a poke around last night. Can confirm the issue, the throttle will randomly fail to respond immediately, and will come back with a jerk. After that if you keep driving there is no low end power and the throttle response is rubbish.
Inpa comes up with code 2A38, valvetronic servomotor: binding or open circuit. No CEL.
We cleared the code, did a relearn for both end stops (which passed OK, can hear motor go from stop to stop) and it seemed to drive fine until it faulted and threw the same code.
At this point we noted in inpa that the live data from the valvetronic motor showed a fixed reading for "VVT actual value" and wasn't moving (like it does when tested straight after an end stop test). Running the end stop test again "freed" it up and it passed fine.
So I'm thinking either it's the valvetronic motor, or maybe the eccentric shaft sensor.
Need Dan to check if there is oil in the connector for the sensor as that's a common failure and oil is a giveaway. Neither part is cheap enough to be shotgunning parts at it.
Anyone had this before?