adjusting knob on the throttle body.

My F-150 has a 5.0L engine. The black knob is on the throttle body. It is easily turned and doesn't seem to have any effect on the idle or anything else that i'm aware of. It appears to be strictly mechanical,no wires or relay attached. I'm not having any problems(that I'm aware of). The truck has 75K miles on it,gets about 15.3 mpg.Auto,air,PS,PB. Driven daily to and from work. That's ir. thanks

In that case close the hood and forget about it!

Forget about what?.................

Adjusting that damn black knob!