The stepper motor is also called ICV (idle control valve), which is exactly what it does.
You may want to clean the stepper motor if you have any of the following:
Hunting (rising and dropping revs)
Please see the below pic for the location of the motor. The Red arrow points to the motor.
To Remove and Clean follow these instructions.
1. Disconnect battery
2. Remove Bolt which the blue arrow points at. (10mm I think)
3. Remove the bolt directly below the above bolt (out of view on this shot)
4. Pull away the unit and disconnect the plug at the back.
5. You now need to take the stepper motor off the housing - just another 2 bolts.
6. You can now clean or replace the motor. I replaced mine but others have cleaned with Carb Cleaner, WD40, or similar de-greaser.
7. Refitting is the reverse of the above.
Reconnect battery and reset the ECU (See Dom's guide)
I also removed the accelerator cable and a few other bits for easy access.
scottri has attached the following image:
________________________________________Ripping up the M1 with M Power.