Honda BF135A - Iab (Intake Air Bypass) Control; System; Iab Control Valve Inspection; Shutter Valve Diaphragm

BF135A•BF150A
5-109
10. IAB (Intale Air Bypass)
CONTROL SYSTEM
• IAB Control Valve Inspection
1. Vacuum line check
-1. Check the vacuum tubes between the shutter valve
diaphragm and IAB control valve, and between the
solenoid valve and intake manifold.
Are the tubes disconnected, torn or clogged?
YES – Replace the vacuum tubes.
NO – Perform "2. Operation check at idling".
2. Operation check at idling
-1. Start the engine and let it warm up. Run the engine at
idling.
-2. Disconnect the vacuum tube from the shutter valve
diaphragm, and check the vacuum.
Is there the vacuum?
YES – Perform “5. Operation check at engine stop
and at high engine speed”.
NO – Go to the step 3.
-3. Disconnect the vacuum tube underside the IAB control
valve, and check the vacuum.
Is there the vacuum?
YES – Perform "3. IAB control valve check".
NO - • Faulty vacuum chamber
• Faulty check valve
3. IAB control valve check
-1. Connect the vacuum tubes.
-2. Disconnect the IAB control valve 2P connector while
running the engine at idling.
-3. Check the vacuum tube located above the IAB control
valve for vacuum.
Is there the vacuum?
YES – Perform "4. Ground line short circuit check".
NO – Replace the IAB control valve.
4. Ground line short circuit check
-1. Turn the ignition switch OFF. Disconnect the ECM con-
nector A and the IAB control valve 2P connector.
-2. Check for the continuity between the No.2 (Black) ter-
minal of the IAB control valve harness side 2P con-
nector and the engine ground.
Is there the continuity?
YES – Repair short in the wire between the ECM
and the IAB control valve.
NO – Substitute a known-good ECM and recheck.
5. Operation check at engine stop and at high engine
speed
-1. Start the engine and run it at idling. Stop the engine
and check the shutter valve diaphragm side vacuum
tube for the vacuum.
Is the vacuum removed?
YES – Perform shutter valve diaphragm check (P. 5-
110).
NO – Perform "6. Signal line open circuit check".
SHUTTER VALVE DIAPHRAGM
INTAKE MANIFOLD
IAB CONTROL VALVE HARNESS
SIDE 2P CONNECTOR
VIEWED FROM THE TERMINAL SIDE
BLACK
VACUUM TUBE