General information
When the engine is idling, the air-fuel mixture is controlled by the Idle Air Control (IAC) system. On Civic models, the system consists of a PCM and an IAC valve, on Integra models, it consists of a PCM, a temperature-sensitive fast idle (FIT) valve, and an IAC valve. The IAC valve is activated by the ECM/PCM, depending on the current engine load (turning on the air conditioner, using the power steering, the temperature of the unit, etc.). the valve regulates the amount of air flow supplied to the intake manifold bypassing the throttle valve. The ECM/PCM receives initial data from the VSS, ECT, PSP switch sensors and the actuation of the A/C compressor clutch. Depending on the current load on the engine, the module adjusts its idle speed accordingly. To avoid disruption of the idle speed stability when starting the engine, the IAC valve opens at the moment of cranking and remains open for some time immediately after starting, providing additional air supply to the intake manifold.
Examination
1. Set the parking brake, chock the vehicle's wheels, and place the transmission in neutral (manual transmission) or "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 operates, then reduce the speed to idle and disconnect the IAC valve electrical connector.
Caution! Avoid touching the fan blades with your hands and avoid allowing hair and loose clothing to come into contact with them. When the valve is disconnected, there should be a noticeable decrease in engine speed, otherwise the valve is most likely faulty. If the speed does drop and the problem with maintaining stability persists, check the condition of the wiring harness and its contact connections between the IAC valve and the ECM/PCM.
2a. Disconnect the wiring from the IAC valve, turn on the ignition (do not start the engine) and measure the voltage between the positive terminal of the connector on the harness side (yellow-black wire terminal) and body weight (see accompanying illustrations): Civic models. The voltmeter should register battery voltage. If there is no voltage, check the condition of the yellow/black wire in the wiring harness between the IAC valve and the PGM-FI main relay. In either case, leave the connector disconnected for further testing.
2b. Integra model valve.
3. If the IAC wiring harness has two wires, connect the valve directly to the battery using two jumper wires (positive terminal - black/yellow, negative terminal - black/blue). The valve should click each time power is applied.
Caution! Do not hold the valve energized longer than necessary to hear the click!
4. If the harness consists of three wires, connect the negative probe of the ohmmeter to the central terminal of the connector, and the positive one to each of the side terminals in turn. In both cases, the device should register a resistance of 16÷28 Ohms.
5. If the checks described in paragraphs 3 and 4 are positive, the vehicle should be taken to a service station for a more detailed diagnosis of the ECM/PCM and the IAC valve circuit.
Replacement
1. Disconnect the electrical wiring from the IAC valve.
2. Remove the two mounting screws and remove the sensor from the air duct pressure chamber (see illustrations above).
3. Installation is carried out in the reverse order. Do not forget to replace the sealing ring.