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HOMESERVICE MANUALSLEXUS1998SC 300REPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTSACOUSTIC CONTROL INDUCTION SYSTEM (ACIS)ACIS SYSTEM CHECKACIS VACUUM SWITCHING VALVE (LS400)
1998 Lexus SC 300

ACIS Vacuum Switching Valve (LS400)

1998 Lexus SC 300SECTION ACIS Vacuum Switching Valve (LS400)
  1. Remove engine cover. Remove battery cover and air cleaner inlet tube. Disconnect throttle body. See THROTTLE BODY in REMOVE/INSTALL/OVERHAUL article. Remove intake manifold assembly. See INTAKE MANIFOLD ASSEMBLY in REMOVE/INSTALL/OVERHAUL article. Remove vacuum tank. Disconnect vacuum hoses and electrical connector from Vacuum Switching Valve (VSV). See Figure-6. Remove VSV if necessary. Measure resistance between VSV terminals. If resistance is 33-39 ohms, go to next step. If resistance is not as specified, replace VSV.
  2. Check for continuity between VSV case and each terminal at VSV connector (this checks for an internal short). If continuity does not exist, go to next step. If continuity exists, replace VSV.
  3. Apply air through port "E". See Figure. Air should flow out of filter, but not out of port "F". Apply 9-14 volts and ground to VSV terminals. Apply compressed air to port "E". Air should flow out of port "F". If ACIS VSV does not function as specified, replace ACIS VSV.
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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.