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Home >> Lexus >> 1991 >> LS 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Exhaust Gas RECIRCULATION (EGR) >> Vacuum Modulator Check
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Vacuum Modulator Check

  1. 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.
  2. 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.
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