Throttle Position Sensor
WARNING: This page is about a different car, the 2002 Mercury Villager. However, it is still accessible from the selected car via links, so may be relevant.
Throttle Position (TP) sensor monitors throttle plate opening. TP signal to PCM is proportional to opening angle. TP sensor is mounted on throttle body, at throttle plate shaft. If Mass Air Flow (MAF) sensor fails, PCM will use TP sensor to provide airflow information. This is called fail safe mode.