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.
1991 Lexus LS 400FACTORY OEM SERVICE PROCEDURE
Fuel Cut System
- Start and warm engine to operating temperature. Ensure A/C is off. Connect a tachometer to engine. Disconnect Throttle Position Sensor (TPS) connector. Using a jumper wire, connect terminals IDL and E2 of harness connector. See Figure.
- Gradually increase engine speed. Observe tachometer as engine RPM is raised. RPM will fluctuate between fuel cut and fuel return points. See FUEL CUT RPM SPECIFICATIONS table.
- If fuel cut system does not function properly, ensure a clearance of .028" (.71 mm) is present between screw and lever on TPS. Ensure wiring harness is okay between TPS connector and ECU connector.
FUEL CUT RPM SPECIFICATIONS
| Application | RPM | |
|---|---|---|
| Fuel Cut | 1800 | |
| Fuel Return | ||
| ES250 | 1200 | |
| LS400 | 1400 | |
Factory Service Tools
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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.
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