Code P0121 - Throttle Position Sensor Circuit Range/Performance Problem: Condition
WARNING: This page is about a different car, the 1995 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
Code is set when ECM consistently detects more than 2 volts from VTA circuit and closed throttle position switch is on. Possible cause is Throttle Position (TP) sensor.