Anyone know?

Ideling a little higher than normal when first started and the engine is cold is normal and in fact necassary with a carbuerated engine. But if it is ideling really fast say over 1000 rpm then you should adjust the fast idle in the side of the carb at the throttle linkage. There is a stepped "cam" there that the idle speed screw rests against that holds the throttle open a little more when the choke is on.

Also it is important to know the correct procedure for starting and warming up a carbuerated engine. Before you crank the engine over you should depress the foot feed to the floor once and then let it up completely. then Crank the engine over and it should start. If it's a completely cold engine or it is very cold out let it set there and idles for about 30 seconds. Then "hit" the throttle sharply about half way to the floor . Don't hold it there just kind of "kick" it. This is called kicking it down. by doing this you take the pressure off that cam I told you about earlier and if the choke is adjusted properly the engine should idle down and the choke should open up at least partially depending on how warm the engine is.At this point you should be able to drive off normally. If it doesn't work properly as I described you may need to work on it or have it worked on. The choke setting on this year of vehicle is riveted to keep people from tinkering with it for emissions reasons. But the rivets can be drilled out and screws installed on the choke housing to allow for adjustments.

It is more than likely your automatic choke they are controlled by temperature so when it is cold the bimetal spring is not at a hot point if it is it will then idle down.

There is an adjustment screw on the right side of the carb under the choke element facing forward. You can turn down the high idle speed. The screw is hard to see under there but its there. I use a pocket screwdriver to turn it. Turn the screw 1/2 turn counterclockise and see if the high idle speed is more to your liking.