If so, how do I go about adjusting it to lower my engine's idle?

Also, what does the IAC valve do? Thanks

 

Yes it does, located on the IM below the TB
You don't adjust it, you adjust the idle screw on the throttle body.
The IAC controls how much air goes to your engine when idling normally, the FITV adds additional air during cold starts.

 

Thanks a lot. Is there a way to check if those valves are bad?

 

Anyone?

 

You could try taking them off and giving them a clean with carb cleaner