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HOMESERVICE MANUALSLEXUS1998SC 300REPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - SYSTEM/COMPONENT TESTSACOUSTIC CONTROL INDUCTION SYSTEM (ACIS)ACIS SYSTEM CHECKINTAKE AIR CONTROL VALVE (LS400)
1998 Lexus SC 300

Intake Air Control Valve (LS400)

1998 Lexus SC 300SECTION Intake Air Control Valve (LS400)
  1. Remove engine cover. Remove battery cover, air cleaner and intake air hose. Remove throttle body. See THROTTLE BODY in REMOVE/INSTALL/OVERHAUL article. Remove intake manifold. See INTAKE MANIFOLD in REMOVE/INSTALL/OVERHAUL article. Install a 3-way vacuum "T" fitting in vacuum hose between Intake Air Control Valve (IACV) actuator and ACIS Vacuum Switch Valve (VSV). See Figure-6. Reinstall intake manifold and throttle body.
  2. Connect a vacuum gauge to vacuum "T" fitting. Start engine. With engine idling, ensure vacuum reading is about 11.8 in. Hg, and IACV actuator rod is pulled out. See Figure. If vacuum is not as specified or actuator valve rod fails to pull out, go to next step.
  3. Snap accelerator to wide open throttle (WOT) position. Vacuum should not exist during wide open throttle and IACV actuator rod should not be pulled out.
  4. Remove IACV. Apply about 11.8 in. Hg to IACV actuator. If IACV actuator rod does not move, replace IACV actuator. If IACV actuator rod moves, check to see if diaphragm holds vacuum for at least one minute. If diaphragm does not hold vacuum, replace actuator. If diaphragm holds vacuum, go to next procedure.
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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.