The intake air temperature sensor measures the temperature of the air entering a car's engine through the intake manifold and relays the information to the engine control unit. To operate as efficiently as possible, car engines rely on the ECU, a small computer, to monitor and adjust various components and processes as conditions change. For example, air is denser in colder conditions, so the ECU must add extra fuel during cold weather to maintain the same fuel-to-air ratio.
A damaged intake air temperature sensor can cause the ECU to either add too little or too much fuel to the engine's fuel and air mixture. This can cause engine misfires, increased emissions, poorer fuel economy, rough idling and surging. An entirely broken intake air temperature sensor causes the check engine light to turn on, but one that is only delivering improper readings might not.
The intake air temperature sensor is located on a car's intake manifold. It may be a stand-alone sensor, or it may be integrated with the mass airflow sensor, which tells the ECU the amount of air that is entering the engine. The sensor works because its electrical resistance varies depending on its temperature. To read the intake air temperature, the ECU sends an electrical pulse through the sensor and calculates how much it has changed when it gets back.