I cannot figure out where the line goes!
85 F150 6 cyl 4 speed OD trans

 

Looks like a vacuum line.. pull the bolt out of the hose while its running … see if it sucks.

 

It looks plugged for a reason you prolly don't need it if it's running good but most vac lines will probably hook up on back of intake to a fitting

 

Is it the same hose coming from the top of the air cleaner? If so then it needs to hook up to vacuum. That thing on the top of your air cleaner is a temp sensor which opens and closes the flap for your air horn sunction. When it's cold out, it closes off some of the air from the cold air side, and sucks warmer air off the exhaust manifold as long as you still have the exhaust shroud. It's meant to help the engine warm up faster and provide a more complete fuel burn during winter months as part of emissions control. Not a bad system, It doesn't rob any power and it does help a little.

 

Read the vacuum map on the core support.


(phone app link)

If you don't understand it, post a good pic of it. If it's missing, you might be able to find it here:
http://www.garysgaragemahal.com/

But all that little system does is pull hot air off the exhaust manifold when it's cold so the engine runs better during warmup. It's not necessary when the weather OR engine is warm.