Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSLEXUS1998SC 300REPAIR AND DIAGNOSISENGINE PERFORMANCEENGINE CONTROLS - ADJUSTMENTSTHROTTLE POSITION (TP) SENSOREXCEPT ES300
1998 Lexus SC 300
Except Es300
1998 Lexus SC 300SECTION Except Es300
- Slightly loosen Throttle Position (TP) sensor mounting screws. TP sensor is located on side of throttle body, facing toward the front of the engine. Slightly rotate TP sensor clockwise. Connect scan tool to data link connector No. 3. See Figure. Turn ignition on.NOTE: Ensure accelerator pedal is not depressed after turning ignition on when adjusting TP sensor.
- Use scan tool to read throttle valve opening which is displayed as a percentage. Throttle valve opening may be read by accessing THROTTLE POS under CURRENT DATA on scan tool.
- While reading throttle valve opening, rotate TP sensor counterclockwise (toward throttle control motor on throttle body) until throttle valve opening is at specified percent. On GS300 & SC300 set specified percent at 15.6, as this is the center of the standard throttle valve opening of 14.4-16.8 percent. On GS400, LS400 & SC400 set specified percent at 15.2, as this is the center of the standard throttle valve opening of 14.4-16 percent.NOTE: When TP sensor mounting screws are tightened, this may cause the throttle valve opening to change. Ensure throttle valve opening remains at specified percent after TP sensor mounting screws are tightened. Readjust TP sensor if necessary.
- Using screwdriver, fully close throttle valve on throttle body. Use scan tool to read throttle opening value by accessing THROTTLE POS under CURRENT DATA on scan tool. With throttle valve fully closed, throttle opening value should be 10-14 percent.
- If throttle opening value is not within specification with throttle valve fully closed, repeat steps 2) through 4) until correct throttle valve opening value is obtained. Turn ignition off. Remove scan tool.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.