The Air charge temperature (ACT) sensor is used by the PCM to determine the temperature and density of air entering the engine. The PCM then uses this information to determine fuel injector control and other outputs. Temperature sensors fail due to simple wear and tear. The sensor connector and wiring harness can lose connectivity over time. Exposure to excessive moisture can erode the sensor internally, causing erratic readings. Symptoms of failure include Poor fuel economy & reduced engine power, rough idle, surging & stalling, black smoke from engine or exhaust, and an overheating engine