With the 'follow tps when not idle' disabled, the stepper should resume the refference position set in the refference table. With 'follow tps when not idle ' enabled, the stepper motor will move its refference position as the throttle is opened, so when the throttle is released, the stepper will return to the refference position gently smoothing the return to idle.
On the Rover Mini, I tune to Rover's specification of - idle advance 15 deg+-5, idle air stepper refference position warm 20 to 40 steps, warm start refference position 80 steps.
Ideally you need to fix the stepper position to 30, and fix the idle advance to 15 degrees, by disabling ignition idle control, then tune the throttle stops to give you your idle speed. Then enable and set the ignition idle control thresholds for 10 degrees advance, 10 degrees retard and IAC degrees to 5.
Stepper motor should not ever be zero, if it is, it needs tuning.
Hope that helps