Idle Up Control Valve: Testing and Inspection

CHECKING BOOST VALVE #1

With the ignition ON, voltage is supplied to boost valve #1 (closest to the battery). If the engine speed drops below 700 rpm, the control unit (relay #3) completes the ground circuit to the #1 boost valve to increase the idle speed. When the engine speed exceeds 1050 rpm, the control unit interrupts the ground circuit to the boost valve.

1. With engine at full operating temperature (80°C/176°F), and idling, turn on all electrical consumers except A/C.
2. Turn in the idle speed adjustment screw (in the throttle housing, facing toward the air flow sensor boot) until the speed drops. At 700 - 750 rpm, the boost valve should open and increase the idle.
3. Pinch boost valve hose closed to drop idle speed back down.
4. Adjust idle speed to 850 - 1000 rpm with boost valve hose pinched closed.
5. Open the boost valve hose. Idle speed should increase and at about 1050 rpm the boost valve should close. Idle should return to previous setting.

CHECKING BOOST VALVE #2

Boost valve #2 is only on cars equipped with air conditioning. The valve is always grounded, and is supplied voltage when the A/C clutch is energized.

1. With the engine idling, and the A/C switched OFF, pinch the idle boost valve hose closed.
2. Idle speed should not change.
3. Switch A/C ON, and with the boost valve hose pinched closed, idle should drop.
4. Open the boost valve hose and idle should return to normal.