......

 

First guess about the leak... Take the master cylinder out and look in the booster.
The Master cylinder could be leaking into the booster.

 

Depending on how much free play you have with the brake line going into the master cylinder...
You might be able to leave the line attached and move the master cylinder out a bit from the booster.
If you can move it out about 2-3 inches, that should be enough for you to take a flashlight and look in there.

 

As for the start up problem. Are you sure the throttle valve is "closed".
Some old cars get gummy in there and don't allow the valve to close "completely".
Take the intake hose off and look and the valve before you start the car and see how much opening there is.

Another idea.. try cleaning out the throttle body intake.
Or adjust the cold choke?

 

If you leave the brake line attached to the Master Cylinder and you are able to move the master Cylinder out (a couple of inches) from the booster to look inside, you do NOT have to bleed the brakes.

As for the "all the stuff", take a picture. you should only have to remove the intake hose to look in the throttle intake.

 

Maybe that was the problem. It was stuck closed after warm up.
So when it cools off, it doesn't open, when it needs to.

Keep us posted. I think we are getting close!

 

After thinking about this more...
1 other thing that can cause high idle is a leaking vacuum line.
Check all the hoses for cracks!

 

Can you take a picture of the master cylinder attached to the Booster?
I would think you can remove 2 nuts, then pull the master cylinder out about 2-3 inches.
You do not need to disconnect the brake line.
You should be able to at least look at the piston/plunger and see if it is wet. ( the part that goes into the booster).