This is the manifold differential pressure sensor, also sometimes incorrectly referred to as a manifold absolute pressure (MAP) sensor.
The MDP sensor measures the amount of vacuum in the intake manifold. It does not do this to measure the amount of air entering the engine. The MDP sensor measurement is instead used to monitor that the exhaust gas recirculation (EGR) emissions control system is working correctly. 1G cars used a temperature probe for this, while 2G cars use the MDP sensor.