The Idle Air Control Bypass Air (IAC BPA) valve consists of an idle air control valve and a bypass air valve.
The bypass air valve functions during cold engine conditions to increase engine idle speed. It consists of a thermowax bead and a valve.
Engine coolant is directed around the thermowax, which opens and closes the valve. During cold engine operation below 140°F (60°C), the thermowax is contracted enough to allow the valve to open. As the coolant heats, the thermowax begins to expand. When the coolant reaches temperatures above 140°F (60°C), the thermowax expands and closes the valve.
The valve controls the amount of throttle valve bypass, which ensures a smooth idle under all engine operating conditions.
- When the engine is cold, air flows through the valve during all modes of engine operation, to maintain the factory set idle speed.
See Figures 1, 2 and 3
- To check the Idle Air Control (IAC) valve resistance, unplug the IAC valve connector.
- Connect a high impedance Digital Volt Ohmmeter (DVOM) to the terminals.
- Measure the resistance.
- The resistance should be 7.7-9.3 ohms.
- If the resistance does not meet specification, replace the IAC BPA assembly.
- To check the BPA valve function, remove the BPA valve from the engine.
- Wait until the valve reaches room temperature. When the valve is cold, blow through the air inlet and verify that air flows freely through the valve.
- Heat the valve with a hair dryer; the air valve should move out and block the passage.
- If the valve does not function as specified, replace the IAC BPA assembly.
- To test the solenoid, connect a scan tool to the Data Link Connector (DLC).
- Turn the key ON and enter the simulation test.
- Access the IACV Parameter Identification (PID) and turn the dial to cycle at 75 degrees.
- Listen for the IAC solenoid to click when using the simulation test.
- If the solenoid clicks it is working properly.
REMOVAL & INSTALLATION
- Disconnect the negative battery cable.
- Drain the coolant until it is at a level below the Idle Air Control Bypass Air (IAC BPA) valve.
The lower coolant line should be disconnected after the valve is separated from the upper intake manifold.
- Tag and disconnect the upper coolant hose from the valve.
- Unplug the valves electrical connector, then loosen the two nuts and two bolts attaching the valve to the upper intake manifold.
- Pull the valve from the manifold and disconnect the lower coolant line from the valve.
- Remove the valve and gasket from the engine.
- Use a scraper to clean any old gasket material from the valve mounting surface.
- Install a new gasket and connect the lower coolant line to the valve.
- Install the valve and its retainers. Tighten the nuts and bolts to 71-88 inch lbs. (8-10 Nm).
- Engage the valves electrical connection and the coolant hoses to the valve.
- Fill the cooling system and connect the negative battery cable.