How do you adjust the throttle sensor and what are the parts if this item.... Or do you just replace it...

 

Throttle position sensor is a variable resistor that lets the computer know what postion the throttle is in. Volvo also has a microswitch that is supposed to be made when throttle is completely closed (click) to let the idle air motor to do its thing. With throttle closed and throttle position loose enough to move turn it until you hear the click, tighten in this position.

 

Also they're relatively inexpensive if you decide to change it.