Diagnosis & Repair
WARNING: This page is about a different car, the 2002 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.
Using Toyota hand-held tester or scan tool, check for any other DTCs. If other DTCs exist, diagnose and repair those DTCs first and retest. If only DTC P0121 exists, replace TP sensor with throttle body as an assembly. See THROTTLE BODY under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.