A manifold absolute pressure sensor (MAP) is one of the sensors used in an internal combustion engine's electronic control system. Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit(ECU). This is necessary to calculate air density and determine the engine's air mass flow rate, which in turn is used to calculate the appropriate fuel flow. An engine control system that uses manifold absolute pressure to calculate air mass uses the speed-density method. Engine speed (RPM)and air temperature are also necessary to complete the speed-density calculation. Not all fuel-injected engines use a MAP sensor to infer mass air flow; some use a MAF (mass air flow) sensor.