I've got no idea what is causing your issues Robbo, like I said, a bit more info about your car is required before you've got any chance of having it diagnosed via the interwebs.
However, while we're taking about Idle Air Control Valves (IACV), The IACV is simply a solinoid with a rubber plunger on the end of it.This is how you clean it.
1) Remove two screws at the front and rear of the unit.
2) Carefully slide the solenoid out of the Throttle Body/ housing, beware that there is a brown o-ring that usually falls out if you're not careful.
3) Spray the knob, housing and shaft wth some UEC (Upper Engine Cleaner) or Throttle Body cleaner and clean it all with a rag/ toothbrush to remove all grimey deposits. (Try to avoid extending or pushing-in the solenoid shaft as the car will struggle to idle correctly for a short period after it's re-installed)
4) re-fit the o-ring to the solenoid.
5) re-fit the soleonid using the two small screws you tried not to drop earlier and remember to plug in the harness connector.
6) test-start engine. You may find the idle erratic/ unstable/ high/ low for a short period of time, your
ECU will soon sort itself out, and you should be fine.
This may not have any influence on your problem at all, but is a half hour job, and worth a shot.