Throttle Position (TP) Sensor: Inspection
WARNING: This page is about a different car, the 1995 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.
Check TP sensor resistance. See THROTTLE POSITION (TP) SENSOR under FUEL SYSTEM in SERVICE & ADJUSTMENT SPECIFICATIONS article. If resistance is not as specified, adjust TP sensor.