assuming everything is hooked up correctly and the engine is in good shape, then I say your engine is either leaning out or richening up as the coolant temp or IAT rises from sitting.
If the wideband shows lean, add some fuel in those temp compensation areas. If it shows rich, take some out.
hood open or hood closed should be able to give you a clue as to if its in the IAT or coolant temp. IE, the IAT sensor will heat soak idling with the hood closed much more quickly than with the hood open.