Im not familiar with INPA, but IIRC with the Bav Tech tool using actual values I was checking the actual position on the eccentric shaft with a nominal position
based on throttle input. It could only be done with the engine running (I think). I had the car in accessory mode and throttle movement reads, but the Servo
stays at rest, so I had to start it after carefully putting the servo back in (scary). Remember if the Servo fails all together the throttle plate swings into action. To see if the Servo is failing slowly maybe you could check if it can go to WOT, hold steady at increments for periods of seconds with no movement, moves as rapidly as throttle inputs, and returns to rest fully. These are
just guesses as I cannot find anything regarding Valvetronic failures other than the servo just fails all together (which is rare supposedly). Maybe a Bently Manual is in order. I'm not sure if you can read values with INPA.