turbo stepper motor??

hi guys, im currently working on a freelander 2 td4. it has lack of power and low boost pressure.

the turbo is off the car and has no play in it at all. happy to say this isnt the fault. but the connecting rod between the turbo to the stepper motor was seized. i have freed this of but when carrying out an actuator test the motor only moves around 4mm before returning to its original position, can anyone direct me as to how much the motor should move and what other problems could be leading to this,

thanks dan