I make a point of setting the idle speed on my aircraft as low as possible as I need to fly into some extremely short strips sometimes. I find that if the engine will just about run during the initial slow running checks, it usually results in a smooth even idle of perhaps 5-600rpm when warm.. just right. Also I have found that with a metal prop, a slightly lower idle can be used.
I say this as a stick and string PFA type, rather as a licensed engineer however..
Kingy