Two possible scenarios. First scenario (most likely) is that the connection to the sensor is lost or the sensor opens up internally, at which point the air temp reading drops to a little below 0 degrees fahrenheit, making the car very rich. Other scenario (not common) is that the connections to the sensor or the sensor itself shorts together, resulting in a 255 degree inlet air temp reading, resulting in a lean condition.
Bad air temp sensor will make the car way rich. My car was tuned mint and then one day if felt slow. so i hooked up the laptop and found my air temp was way off and my a/f was 9.79 to 1 took out the sensor and it was gone(the guts) replaced it problem gone.