Button, the IAT is the incoming air temp. It effectively measures the amount of air coming in. Cold air is denser than warm air so colder IAT is like getting more air in. The map then adjusts fuelling to match this, more fuel for colder air. This creates a slightly more powerful explosion in the cylinder and small power increase. A simplified description! Another analogy is cold starting with a choke on carb engines. Cold air, increased fuel, engine runs. As the engine warms up remove choke (either auto as it senses a temp increase) or just push in the choke cable. My Plus8 has Gems management and uses sensors/ evap cannister to imitate the choke method when cold by triggering fuel input from the map to suit cold air, coolant etc.. As the engine warms it moves fuel input to a different point on the map to suit conditions.
