As I said coolant temp causes the ECU to adjust all three of those things but sticking to idle speed control and without going into great detail it works like this:
The ISCV is fully open upon start because it went to full open when the engine was last shut down. To avoid too high of an idle speed when the engine starts the ECU will begin to command the ISCV closed when engine rpm crosses 500. Where the valve stops depends on coolant temp and a few other things (oil pressure for example) with coolant temp being the dominant variable. Thereafter, as coolant temp warms, the valve continues to close from that point until coolant temp reaches 70 C. At that temp fast idle control ends and the system enters feedback mode.
Feedback control is +/- 20 rpm of target but target will change depending on several things. The system also develops a learned value much like fuel control does. It's why resetting the ECU causes some cars to idle a bit weird until the ECU relearns the new value. Course, that only happens if something is worn or mis-adjusted, same as happens with fuel control.
This is where the myth of "resetting the ECU fixed my problem" stems from. The bottom line is if the engine is in good shape and everything is working correctly there will be no (or a very slight) learned value and the engine will run exactly as it did before the reset, which means correctly. Make sense?
All that said your problem most likely isn't electronic. The ISCV and check valve may need cleaning though. The first thing I would do is make sure the valve is stepping full open upon shut down and the check valve is working. Since they provide the only idle air path the engine has (other than the PCV system), and since the path is capable of allowing idle speeds of nearly 2000 rpm, something must be wrong along it somewhere.
