The intake air temperature sensor is integrated in the mass air flow sensor on most modern engines. The change in resistance with a temperature increase or temperature decrease is used to convert the temperature into a measured value that can be electrically evaluated by the digital engine electronics control unit.
The intake air temperature sensor is required for the start procedure in conjunction with the engine coolant temperature sensor. The resistance values of both sensors supply exact information for calculating the injection timing. In this way hot start problems in particular are avoided.
During the start procedure, the temperature sensors are therefore used as a measured variable up to a freely programmable engine speed threshold.
The air column in the mass air flow sensor can oscillate during the start procedure. For this reason, the value output by the mass air flow sensor cannot be used as a correct value for injection timing.