My plugs have a gray residue on them, which would tell me its running too lean. That would indicate to me that the IAT resistor override does actually affect the amount of fuel injected when the engine is in closed loop, normal operation.
Otherwise, as others have said, the O2 sensors would have forced the mixture to 14.7 to 1. There is no way the plugs would have the gray deposit if that was true, IMO.
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