First timer

Howdy gents, I'm a first timer here so thanks for having me. I'm going to go ahead and just post my issue here and someone can tell me where to stick it.I got a 1990 fuel injected toyota pickup 2X4 22RE and ive been through it a little bit and she runs perty good although the idle seems to be a bit off. sometimes it will idle low and sometimes it will idle higher. sometimes but quite rare it will fluctuate a bit. So i ask you, is there a way to adjust the ration to tune it in better? what is the black turnable knob accessable from the top of the engine? What are the two or three vacuum operated sensors on the top of the valve cover?