I noticed today that a vac line broke off from the throttle body. It looks like it is right behind the IAS and there are 2 of them one on each side. When I cover it up with my finger the idle will drop and when I hold the hose back on it does the same thing. What is that for?

 

From the picture, I can't really get a good idea of where it's at. No matter where it is, a vacuum leak will make your engine run like crap. Those lines are cheap at the auto parts store and simple to cut to length and replace.

Those lines could control some of your emissions solenoids, the MAP sensor, etc. Your power brakes, cruise control, some distributors, and some transmissions use vacuum too (although I don't think those are the lines in question).

 

I would just replace them with fresh lines they only go to a block on the other side of the intake manifold. Not to sure on what they do.

 

Those two lines hook to the vapor canister and draw the gasoline vapors from the gas tank to be burned. The truck will run better with them hooked up or at least capped off.