What is this vacuum line for?

[67drake]

Putting my newly rebuilt engine in I noticed a line that I’m just curious what it is for. The car is a ‘62 Mercury Meteor.
It runs from a fitting up by the throttle cable, runs along the top of the intake manifold, then down to the power steering pump. I can’t figure out why a vacuum line would run to the PS pump.
What is this for?
Thanks

 

[KULTULZ]

It is a CARB IDLE SPEED-UP VALVE (hydraulic).

 

[67drake]

Ah! Thanks!
In the 40 years I’ve owned the car, I’ve never adjusted or paid any attention to it. Now that I’m putting it back on my engine I was thinking “What IS this?”