really high idle on cold start

[DRobb's_85]

Ok, normally when I start my truck up cold it will idle around 1100 or 1000 rpm for a minute or two and then with the tap of the throttle goes down to normal warm idle. Well today after school I cranked it up as usual and instead it revved all the way up to 1900 or 2000 rpm and would not come down until i waited a few minutes and tapped the throttle, which it then came down to the normal warm idle. For those few minutes I thought it was gonna blow up, everybody was staring at me like what are you doing hah..Anyways, its done this to me just a few times in the past, hardly ever happens. But I'd like to figure out why its doing this, I dont like it revving like that when its cold..Could it be the choke maybe? By the way, its an 85 k10 with 350 and a relatively new edelbrock 1406 carb.