Yup, it's frustrating to chase a problem that is affected by many things...Just look how many responses you get on the search "rough Idle".
I recall a posting maybe 2 months ago where the idle was finally fixed by adjusting the valves. One valve was out of spec...
Here's another easy one, cleaning the idle control valve. When pulling the connector to it, idle should increase to over 2000 rpms.
It and the connecting tubes can be cleaned for smoother operation. It is easier once the air filter housing is off.