A bad mass air flow sensor in a vehicle makes starting difficult and affects the performance of the engine because he engine-control unit uses data from the MAF sensor to balance the fuel ratio the injectors deliver to the engine. A bad sensor returns a significantly different temperature than that of the engine coolant when read using a scan tool set to temperature.
The MAF sensor uses the temperature difference between the coolant and air entering the fuel mix to determine airflow. Under normal circumstances, the temperature of the air is a few degrees cooler than the coolant. If the sensor is bad and displays a temperature higher than the coolant level, the engine-control unit reduces the fuel flow, resulting in a lean operating condition that decreases fuel economy. If the temperature is reading too low, the unit sends too much gasoline, causing a rich operating condition, which also decreases economy.
Sometimes MAF sensors return bad temperatures due to an accumulation of dirt around the sensor. Cleaning the unit involves soaking it in rubbing alcohol in a plastic zipper bag. After cleaning, the unit requires about 20 minutes to dry before reinstallation. Most automobile parts stores carry cleaning kits for these sensors. When cleaning the units, owners should be cautious of the leads, which cannot be repaired if broken, necessitating replacement of the unit.