Without knowing what year vehicle you have, here is a shot in the dark. Warm up the engine thoroughly. set idle to specified rpm. while looking at the tach adjust each idle mixture screw for maximum rpm. Screw each idle mixture screw in 1/4 to 1/2 turn in from max rpm value. In the old presmog days you would have left them at max. Reset idle speed to specs. The above procedure does not apply to computer controlled carburetors.
