Diagnostic Procedure
WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.
Check the vehicle speed sensor. See COMBINATION METER CIRCUIT PLATE under CIRCUIT TESTS in appropriate INSTRUMENT PANEL article. If the results are OK, check and replace the cruise control ECU. See CRUISE CONTROL ECU under REMOVAL & INSTALLATION. If the results are not OK, replace the vehicle speed sensor. See VEHICLE SPEED SENSOR under ENGINE SENSORS & SWITCHES under appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE.