So its an 85 right? and you have a Quadrajet on it right? My guess is that the choke isn't working/adjusted right, What will happen, cause mine does this every now and then when its cold, is the choke doesn't open all the way so the carb thinks the engine is cold, and then sticks into high idle, when you blurp teh throttle you pop it off teh high idle cam and back down to normal, so check out the choke, Now of course this is only a theory /forums/images/icons/grin.gif