Intermittent High idle

My 2001 chevy Astro was repaired for a random miss on all cylinders in the engine. They replaced the entire distributor, rotor, cap, plugs, and I replaced the coil before the shop worked on the van. The miss is totally gone but now it wants to idle high. This does not happen all the time as when cold it operates just fine. After it runs a little while and starts to warm up it drives with out touching the gas at 35 mph because of idleing fast. After parking and not touching the gas it will idle down to normal idle speed within a minute or two. If during this time I touch the gas or the ac compress kicks in it will idle fast again. I checked the trottle and it is not sticking. Is this a computer or sensor issue? I want to try to fix this myself instead of getting raped at a dealer.