What happened was, I picked up my car from the mechanic yesterday after they reconditioned the alternator. On my way home, the car suddenly stalled on the roundabout. Drove it back to the mechanic and they said the ECU has reset itself as they took off the negative lead on my battery (is it true? they have to disconnect the battery?)
I drove around 30 minutes from kingsford to north ryde this morning, it did not stall anymore but the idle keeps hunting every time I put the car into neutral or when the fan kicks in, sometimes it goes down to nearly 0 and comes back up to around 5 - 600 (no warning lights came on).
I was thinking the stepper motor could be dirty or the ECU was not reset properly yesterday (Mr. Prez, I heard you work around North Ryde area, maybe you could have a look at it)

I'll try to clean it up and reset the ECU again tonight.
For the time being, anyone knows where to get the Clutch Slave Cylinder and Stepper Motor (in case I have to replace it) and how much?