DTC 51: Idle Signal Circuit: Notes
WARNING: This page is about a different car, the 2002 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Ensure Throttle Position (TP) sensor adjustment and operation are normal. See ON-VEHICLE ADJUSTMENTS - V6 & V8
article in ENGINE PERFORMANCE. Adjust or replace TP sensor as necessary.