Idling matters

Apart from having certain errands being forgotten, I had my car undergo an MUT check (possibly tuning) but halted when I was informed the idling stepper controller (or idling stepper motor) possibly out of order.

Without A/C (Normal: go around 12++ step)
On Idle: 0 step
Idle with 2nd fan initiated: 0 step

With A/C (Normal: go around 60++ step)
On Idle: 17 step
Idle with 2nd fan initiated: 39 step

These are readings from MUT-II, and standard figures based from the attending mechanic's explanation.
















Stepper motor | Throttle opening | Idling motor

As advised, few possibilities might have contributed this error:
1. Bad wiring
2. Dirty ISC
3. Disfunctional ISC