Idle Up Control Valve: Testing and Inspection

Idle Boost Valve:

Idle Boost Valve Hose Diagram:

1. The Idle Boost Valve (called boost valve I) is a solenoid valve controlled by an electronic control unit on the fuse/relay panel that turns the valve ON and OFF according to an engine speed signal from the ignition coil. A control unit signal opens the valve below:

750 rpm

2. The valve should open with an audible click. When engine speed exceeds:

1050 rpm

3. The control unit opens the circuit and the valve closes. The second boost valve on cars with air conditioning (called boost valve II) is switched ON and OFF at the same time as the air conditioning compressor.
4. If the Idle Boost Valve I does not respond as specified, check that approximate battery voltage (12VDC) is reaching the valve at the black wire of the harness connector when the ignition switch is ON. If voltage is not present, see the current flow diagrams for help in troubleshooting the wire. Check the ground at the brown/black wire of the harness connector when the engine speed is below approximately:

750 rpm

5. If there is continuity below this speed and the valve is not opening, the valve is faulty and should be replaced. If there is no continuity to ground, check the signals to and from the control unit as described below.
6. Using the terminal numbers on the back of the control unit as a guide, test at the fuse/relay panel sockets. Test for continuity to ground at the socket for terminal 31. With the ignition switch ON, check for battery voltage (approximately 12 VDC) at the socket for terminal 15a. With the engine running, test for voltage between the socket for terminal 1 and ground. Also check the continuity of the wiring at the socket for terminal 87 and the brown/black wire of the valve's harness connector. If no wiring faults are found, and the system does not function properly, then the control unit is faulty and should be replaced.
7. On cars with air conditioning which have a second boost valve (boost valve II) the valve is always grounded. It receives battery voltage and boosts idle speed whenever the A/C is switched ON. Test the boost valve II by switching the A/C ON, then disconnect the harness connector from the valve. Idle speed should drop as the boost air is cut OFF.