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
Vacuum Modulator Check
- Turn engine off. Label and disconnect all vacuum hoses from EGR vacuum modulator. Block ports "P" and "R" with finger (twin ports on side of modulator). See Figure. Blow air into port "Q" (single port on side of modulator). Air should flow freely out of filter.
- Start engine, and run it at 3500 RPM on ES250 or 2500 RPM on LS400. Block ports "P" and "R" with finger. Blow air into port "Q". Air should not flow out of filter. If air flows out of filter, replace EGR vacuum modulator.
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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