In searching for information on our 2002 Expedition's MAF and IAT circuits, I pulled this out of our new subscription to Mitchell's ProDemand. WONDERFUL package, by the way!
So, here's everything you need to know about these units-with ONE notable exception. In our engine, it uses an additional sensor inside the intake to determine the Manifold Air Temperature. For us to successfully alter the IAT, we will need to address both.
Still, the information here taught me, so I figured a few of you might benefit as well.
Operation of the Combined MAF IAT Sensor
Mass Air Flow (MAF) Sensor
The mass air flow sensor (MAF) measures the mass of air flowing into the engine. The MAF sensor output signal is used by the powertrain control module (PCM) to calculate injector pulse width. For transmission strategies the MAF sensor is used to regulate electronic pressure control EPC, shift and torque converter clutch scheduling.
Mass Airflow Sensor
Mass Airflow (MAF) sensor is located between air cleaner and throttle body, or inside air cleaner assembly. MAF sensors use a hot wire sensing element to measure amount of air entering the engine. Air passing over the hot wire causes it to cool. The hot wire is maintained at 392°F (200°C) greater than ambient temperature, as measured by a constant cold wire. See Fig 1.
The current required to maintain hot wire operating temperature is proportional to the intake air mass flow. MAF sensor outputs an analog voltage signal to PCM proportional to intake air mass. PCM uses this signal to calculate fuel injector pulse width in order to provide the desired air/fuel ratio. On some applications, MAF sensor input is used in determining transmission Electronic Pressure Control (EPC), shift and Torque Converter Clutch (TCC) scheduling.
Cougar 2.0L, Escort 2.0L 4V, Econoline, Escape, Explorer, Focus, Mountaineer, Sable, Taurus and Windstar applications use MAF sensors that have Integrated By-Pass Technology (IBT) with an integrated Intake Air Temperature (IAT) sensor.