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Intake Air Bypass (IAB) Control System: Testing

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1999 Acura NSX-T, 1999 Acura NSX, 1998 Acura NSX-T, 1998 Acura NSX, and 1997 Acura NSX-T. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION: Do not adjust the IAB control valve full-close screw. IAB control valve is preset at the factory.
  1. Check the IAB control valve shaft for binding or sticking.
  2. Check the IAB control valve for smooth movement.
  3. Check that (A) of the IAB control valve is in close contact with the stopper when the vacuum hose is disconnected from the IAB control diaphragm. See Fig 4 .
  4. Check that (B) of the IAB control valve is in close contact with the full-close screw when you apply 15 in. Hg (380 mm Hg) of vacuum to the IAB control diaphragm. See Fig 5 .
  5. If any fault is found, clean the linkage and shafts with carburetor cleaner.
  6. If the problem still exists after cleaning, disassemble the intake manifold and check the IAB valve body assembly. See NSX & NSX-T 3.0 & 3.2 LITER article.
Fig 1: Intake Air Bypass (IAB) System Schematic
G00097418Courtesy of AMERICAN HONDA MOTOR CO., INC.
Fig 2: IAB Control System Diagnostic Flow Chart (1 Of 2)
G00107056Courtesy of AMERICAN HONDA MOTOR CO., INC.
Fig 3: IAB Control System Diagnostic Flow Chart (2 Of 2)
G00107057Courtesy of AMERICAN HONDA MOTOR CO., INC.
Fig 4: Identifying IAB Control Valve Open Position (No Vacuum)
G00107050Courtesy of AMERICAN HONDA MOTOR CO., INC.
Fig 5: Identifying IAB Control Valve Closed Position (Vacuum Applied)
G00107051Courtesy of AMERICAN HONDA MOTOR CO., INC.
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