GS430 & LS430
WARNING: This page is about a different car, the 2003 Lexus SC 430, 2003 Lexus LS 430, 2003 Lexus IS 300, 2003 Lexus GS 430, and 2003 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect Throttle Position (TP) sensor 4-pin connector. See Fig 1. Measure resistance between terminals VC and ETA at TP sensor. Resistance should be 1250-2350 ohms at 68° F (20° C). If resistance is not 1250-2350 ohms, replace TP sensor.