Is this supposed to be connected?
 

Ok, what is this, and why isn't it connected to something? The end seems too clean to have been like that since new and the end is bulged a little at the end as if a plug were in it.

https://i365.photobucket.com/albums/...h_100_0839.jpg

https://i365.photobucket.com/albums/...h_100_0840.jpg

https://i365.photobucket.com/albums/...h_100_0841.jpg

I've been having idle problems with my blazer for awhile and everyone keeps telling me to check the vac hoses, well i went out and did that today and found this one. I have no idea what it is or where it goes. any help is much appreciated!

That appears to be the hose to your PCV valve?
Is there a diagram under the hood?

ahhh, yes thank you much! There was a little diagram that had it labeled as PCV air in and it was showed connected to the air box. I found the little outlet and plugged it back in. Should that have a clamp on it? or just leave it free? And i don't suppose that would have anything to do with my crappy idle?

Definitely affects idle. You had a major vacuum leak with that disconnected.
How tight does is fit to the fitting on the air box? If it's pretty snug should be fine.

How much does that affect idle? Would it cause the rpm's to drop when i shift into gear? because that's what i'm experiencing. I drove it after i connected it and it didn't seem to make too much of a difference. I'll go start it up and let it run in the driveway. Before i connected it, i ran it and the engine rpms would rise and drop constantly so i could watch the engine shake and vibrate pretty good. I didn't let it idle and watch it after i connected it though. i should have done that.

RPM's will drop when you shift into gear. That's normal. (Assuming you're not stalling.) While you're at it you may want to go ahead and replace that PCV valve if it's been awhile....they're like $4.00.

well, see that's the thing, it drops almost low enough to stall. it makes the truck shake and then usually go back up. I went out and ran it, and it idled fine in park and while in drive. given, it's warm now. That may make a difference but the stalling seems to be random at best.

Edit: and i'll look into replacing that valve. Although im sure the shop i brought it to a few months ago would've checked that to make sure it was fine.