Sounds like a vacuum leak, though your float level within the carburetor could be out of whack (try whacking the top of the carb with a screwdriver handle when it's idling high, sometimes Holley/Weber/Motorcraft 5200 floats just hang for some weird reason, I rebuilt mine three times then switched to a Motorcraft 2100 (involves a bit of fabrication and giving up having a choke, not worth it on a street-driven car) If it's not a vacuum leak or a sticking or out-of-adjusment float I'd be at a loss for an idea as to what it was.
__________________ 1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4 tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".) | 
Problem with a 2.3L Carburetor 
