Once the car is warmed up, the car should be idling on it's base setting, about 850/900rpm acheived with the screw on the underside of the throttle housing, with ISCV disconnected, lights etc OFF, then when you reconnect the iscv the revs raise a few seconds then go to base setting.
The iscv is to raise the revs at idle when loads such as lights etc are applied(alternator drag).
No it will do no harm not having it connected you just lose the fast idle facility.
tabetha