I have an 86 z28 and I'm having an idleing problem. When I start the engine it idles at 2500 rpm. Within about 5 minutes it rises to 3000 and seems to just keep climbing from there. Ive been told it could be the choke, a vacume leak or a problem with the carburetor witch is a 2 barrel rochester quadrajet. Any advise would be greatly appreciated!!!