Neither of the above, defo a problem with the base idle which is controlled mechanically with the means of a screw which is located on throttle body, it is secured by a lock nut which needs to be loosened first and if not tightened properly will fall out and so you have no base idle which may be what has happened.

The ISCV job is to raise idle speed ABOVE base idle when desired, nothing else.

Idle should be around 950RPM when hot with ISCV disconnected. If the screw is there try adjusting clockwise to increase idle speed.

Martin