A useful analytical tool is to get the car well up to temp (say after a run) and disconnect the electrical plug from the IACV. Check what the car is idling at. It should be 850 ish. If it's markedly different, then, when connected, the IACV will be constantly working to try to bring it to that figure.
A sticking high idle speed can be down to a high base idle setting. It can also be that the accelerator cable is frayed and sticking in its sheath. So check the cable is moving smoothly and allowing the throttle body to close properly.
If the base idle is too low you can get hunting. ie the revs drop low and suddenly pick up and then drop again. In other words the IACV is hunting for the right idle speed. Usually you get a lot of stalling.
David