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Throttle System Operation (GS300 & SC300)

  1. Ensure all accessories are off. Ensure throttle linkage moves smoothly. Turn ignition on. Rotate accelerator pedal position sensor lever and listen for running sound from throttle motor. Ensure friction sound does not exist. If running sound exists, go to step  3. If running sound does not exist, go to next step.
  2. Check throttle control motor. See THROTTLE CONTROL MOTOR  under MOTORS, RELAYS & SOLENOIDS. Replace throttle control motor as necessary and retest. If throttle control motor is okay, check for open or short circuit in wiring harness between throttle control motor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary. If wiring is okay, ECM may be defective. Check ECM. See PIN VOLTAGE CHARTS article. Repair as necessary.
  3. Connect Lexus scan tool to Data Link Connector (DLC) No. 3. See Figure. Using scan tool, select CURRENT DATA. Rotate accelerator pedal position sensor lever to full open position. Throttle opening percentage (THROTTLE POS on Lexus scan tool) should indicate 60 percent or more. If results are as specified, go to step  5. If results are not as specified, go to next step.
  4. Check accelerator pedal position sensor. See ACCELERATOR PEDAL POSITION SENSOR  under ENGINE SENSORS & SWITCHES. Replace accelerator pedal position sensor as necessary and retest. If accelerator pedal position sensor is okay, check for open or short circuit in wiring harness between accelerator pedal position sensor and ECM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary. If wiring is okay, ECM may be defective. Check ECM. See PIN VOLTAGE CHARTS article. Repair as necessary.
  5. Start engine. Allow engine to reach normal operating temperature. Ensure all accessories are off. Place transmission in Neutral position. Turn A/C on and then off and check idle speed. Idle speed should be between 700-800 with A/C on. Idle speed should be between 650-750 with A/C off.
  6. With engine idling, pinch air assist hose located next to throttle motor. Idle speed should drop and return back to normal. If idle speed changes as specified, no problem is indicated at this time. If idle speed does not change as specified, check throttle body. If throttle body is okay, check for open or short circuit in wire harness. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary. If wiring is okay, ECM may be defective. Check ECM. See PIN VOLTAGE CHARTS article. Repair as necessary. After repair is completed, drive vehicle to ensure vehicle performs properly.
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