General information
When the engine is idling, the air-fuel mixture is controlled by the idle speed stabilization valve (IAC). The IAC valve is activated by the PCM, depending on the current engine load (air conditioning on, power steering on, engine temperature, etc.). The valve regulates the amount of air flow supplied to the intake manifold bypassing the throttle valve. The PCM receives initial data from the VSS, ECT, PSP and A/C compressor clutch sensors. Depending on the current engine load, the module adjusts the engine idle speed accordingly. To avoid disruption of idle speed stability when starting the engine, the IAC valve opens when the engine is cranking and remains open for some time immediately after starting, providing additional air supply to the intake manifold.
Examination
Caution: When working in the engine compartment, try to keep hands, hair and clothing away from moving components such as drive belts, fan blades, etc.
1. Set the parking brake, chock the vehicle wheels and shift the transmission into neutral (manual transmission) or into position "P" (automatic transmission). Connect a tachometer to the engine in accordance with the manufacturer's instructions. Start the engine and increase its speed to 3000 rpm. Wait until the cooling fan starts, then reduce the speed to idle and record the tachometer readings (the cooling fan and all electrical consumers must be switched off). If the crankshaft speed is 650-700 rpm, the system is functioning properly. If the measurement result is below 650 rpm, disconnect the electrical connector of the IAC valve. When disconnecting the valve, there should be a noticeable decrease in engine speed, otherwise the valve is most likely faulty. If the RPM drop occurs and the problem of maintaining RPM stability persists, check the condition of the wiring harness and its connections between the IAC valve and the PCM.
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2. If the tachometer registers a value greater than 750 rpm, stop the engine and disconnect the air intake duct from the throttle body. Run the engine at idle speed. Block the lower port of the throttle body (connected to the IAC valve) with your finger - if the speed drops noticeably, adjust the idle speed setting to match the requirements of the Specifications (see Chapter Settings and ongoing maintenance). If adjustment fails, replace the IAC valve. If there is no drop in speed, check the intake tract for signs of vacuum loss.
3. If the test confirms that the IAC valve is working properly, but the problem with the instability of speed remains, check the condition of the electrical wiring and its contact connections in the area between the valve and the PCM.
4. Check for proper battery power to the IAC valve. Disconnect the wiring from the valve, turn on the ignition (do not start the engine) and measure the voltage between terminal No.2 of the harness side connector and ground. The nominal value is equal to battery voltage. If there is no power, check the condition of the wiring in the circuit between the IAC valve and the PGM-FI main relay (see the wiring diagrams in Chapter On-board electrical equipment).
5. Using an ohmmeter, measure the resistance between terminal 1 of the IAC valve and ground. The device should register continuity, otherwise, perform restorative repairs to the ground.
6. If the results of both tests are positive, take the car to a service station for more detailed diagnostics.
Replacement
1. Disconnect the electrical wiring from the IAC valve.
2. On V6 models, remove the throttle body from the intake manifold (see Chapter Power and exhaust systems).
3. Remove the two mounting screws and remove the valve from the intake manifold (4-cylinder models) or throttle body (V6 models).
4. Installation is carried out in the reverse order. Do not forget to replace the sealing ring.
(The text can be found on the website: HONDABOOK.ru)