This one is still eluding me! To date we have:

Reflashed the ECU with the latest software
Replaced the valvetronic actuator motor with a known good one (& relearned stops)
Renewed the eccentric shaft sensor
Swapped the cam sensors over
Confirmed physical cam timing is OK
Swapped the vanos solenoids over
Checked each coil pack
Changed the plugs
Cleaned the MAF
Renewed the PCV
Smoke-tested the inlet system
visually checked the cams & valvetronic shafts for damage

...all of which have made no difference!

If starting the car with the valvetronic motor disconnected the car will idle smooth-as-you-like (valvetronic in 'limp mode' and valves @ 9.5mm lift), untill you plug the motor back in then it all goes lumpy again. Valve lift is then around 0.69mm on idle and no fault codes are being logged.

Any suggestions or pointers?