General information
When the engine is idling, the air/fuel mixture is controlled by the idle speed control valve (IAC). The IAC valve is activated by PCM command, depending on the current engine load (turning on the air conditioner, using the power steering, unit temperature, etc.). The valve regulates the amount of air flow supplied to the intake manifold bypassing the throttle. The PCM receives initial data from the VSS, ECT sensors, PSP sensor-switches and the operation of the A/C compressor clutch. Depending on the current load on the engine, the module adjusts its idle speed accordingly. To avoid idle 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 to the intake manifold.
Examination
Attention! When working in the engine compartment, be careful to keep hands, hair, and clothing away from moving components such as drive belts, fan blades, etc.
1. Engage the parking brake, chock the vehicle's wheels, and shift the transmission into neutral (RKPP) or in position "R" (AT). Connect a tachometer to the engine according to the manufacturers instructions. Start the engine and raise its speed to 3000 rpm. Wait for the cooling fan to operate, then reset to idle and record the tachometer reading (the cooling fan and all electrical consumers must be turned off). If the crankshaft speed is 650÷700 rpm, then the system is functioning properly. If the measurement is below 650 rpm, disconnect the IAC valve electrical connector. When the valve is disconnected, a noticeable decrease in engine speed should occur, otherwise the valve is most likely defective. If there is a drop in speed, and the problem with maintaining their stability does not disappear, check the condition of the wiring harness and its contact connections in the area between the IAC valve and the PCM.
2. If the tachometer reads more than 750 rpm, stop the engine and disconnect the intake duct from the throttle body. Run the engine to idle. Block the bottom port of the throttle body (connected to IAC valve) finger, - if the speed drops noticeably, adjust the setting of their idle value, bringing it in line with the requirements of the Specifications (see chapter Settings and ongoing maintenance). If the 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 check confirms that the IAC valve is working, however, the problem with the violation of the stability of the revolutions remains, check the condition of the electrical wiring and its contact connections in the area between the valve and the PCM.
4. Verify that the battery power supply to the IAC valves is working properly. Disconnect the electrical wiring from the valve, turn on the ignition (do not start the engine) and measure the voltage between the No. 2 harness side connector terminal and ground. The nominal value is equal to the battery voltage. If there is no power, check the condition of the wiring in the section of the circuit between the IAC valve and the PGM-FI main relay (see wiring diagrams in Chapter Onboard electrical equipment).
5. Using an ohmmeter, measure the resistance between terminal 1 of the IAC valve and ground. The device must register the presence of conductivity, otherwise, carry out a ground repair.
6. If the results of both checks are positive, drive the car for more detailed diagnostics to a service station.
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. Turn out two fixing screws and remove the valve from the inlet pipeline (4-cylinder models) or throttle body (V6 models).
4. Installation is carried out in the reverse order. Don't forget to replace the o-ring.