The Intake Air Temperature Sensor (iat) is actually the same as the Manifold Air temperature Sensor (mat). General Motors just changed the name.
The Intake Air Temperature (iat) sensor is a thermistor mounted in the intake manifold. A thermistor is a resistor which changes resistance based on temperature. Low manifold air temperature produces a high resistance (100,000 ohms at -40°F/-40°C), while high temperature cause low resistance (70 ohms at 266°F/130°C).
The ecm supplies a 5 volt signal to the iat sensor through a resistor in the ecm and monitors the voltage. The voltage will be high when the manifold air is cold and low when the air is hot. By monitoring the voltage, the ecm calculates the air temperature and uses this data to help determine the fuel delivery and spark advance. A failure in the iat circuit should set either a Code 23 or Code 25. Once the trouble code is set, the ecm will use an artificial default value for the iat and some vehicle performance will return.