Can it be done mecahnically? how?

Since replacing my PCV the car is still idling fast, had a good check for air leaks and can't find any, car is holding its revs ok too. My old man suggested the theory that beacuse the airways are cleared from the new PCV, then more air is getting in through the proper channels so it may just need adjusting...

Firstly, is that theory at all plausable?
And secondly, is the idle controlled mechanically/electronically - ie is the screw stop on the throttle linkage designed to control the idle or is it an ecu feature?.
Is adjusting the idle as simple as adjusting the screw or not?

Ta,
Rich