Well, time to delve into this a bit more. Ford or Chevy? Carb model? Lets assume for a moment that it is a 5.7, 350, Merc 260 with a Quadrajet. You can manually move the heat riser linkage to simulate warm up, then crack the throttle to see if the high idle cam backs down, it should. Another issue very common to Qjets is the throttle shafts on the primaries wear out and introduce a nasty vacuum leak around the throttle plate. Makes for a lean and high idle condition. Not running, if you can wiggle the throttle shaft then its time to re-bush the shafts. Its not the shaft that wears, its the soft aluminum body of the carb itself. Kits comes with the drill bit, bushings, and Loctite. Just a thought, could be the shaft or linkage binding somewhere. You should be able to manipulate the linkage without it running to see if the throttle plate returns to normal position.