Idle control system and idle speed control valve testing

First, the idle speed control system on the car can be tested using three different methods, and the most suitable one should be selected based on the situation. (1) Checking the engine idle after starting. When the engine is started in a cold state, the idle speed should reach the specified fast idle speed (usually around 1500 rpm) during the warm-up process. Once the engine reaches normal operating temperature, the idle speed should drop to the standard level (typically 750 rpm). If the idle speed doesn't follow this pattern, there may be an issue with the idle speed control system. Additionally, when the air conditioner is turned on after the engine has warmed up, the idle speed should increase to approximately 900 rpm. If it doesn't, the system might be faulty. While the engine is idling, if you slightly adjust the idle speed screw, the engine speed should remain unchanged. If it does change, it suggests that the idle speed control system is not functioning properly. (2) Testing the idle speed control valve's operation. For a pulse linear solenoid valve, disconnect the harness connector while the engine is idling and observe if the engine speed changes. A change in speed indicates that the valve is working correctly. For a stepper motor type idle control valve, listen for a brief "buzzing" sound after the engine is turned off. This sound indicates that the motor is functioning properly. Another way to test a stepper motor valve is to unplug its harness before starting the engine and then plug it back in once the engine starts. If the engine speed changes, the valve is working; otherwise, there may be a fault in the valve or the control circuit. (3) Checking the ECU control voltage. For a pulse linear solenoid valve, disconnect the harness connector and use a multimeter to measure the terminal voltage. If the ECU outputs a pulse voltage during engine operation, the system is likely working. If no pulse voltage is detected, turn on the air conditioner and retest. If the problem persists, check the wiring between the ECU and the idle speed control valve for any open circuits or poor connections. If the wiring is fine, the ECU itself may need to be replaced. Second, testing the idle speed control valve: (1) Measuring the coil resistance of the idle speed control valve. Remove the valve and use a multimeter to measure the resistance of the coils. A pulse linear solenoid valve typically has one set of coils with a resistance of 10–15 ohms, while a stepper motor type usually has two to four sets of coils, each with a resistance of 10–30 ohms. If the measured resistance is outside this range, the valve should be replaced. (2) Testing the operation of the stepper motor. Connect the battery power to the coils in a specific sequence to make the motor rotate. The layout and wiring of the coils vary depending on the model. As an example, take the 2JZ-GE engine's idle speed control valve on a Crown 3.0 sedan. First, connect terminals B1 and B2 to the positive battery terminal, and then connect S1, S2, S3, and S4 sequentially to the negative terminal (S1-S2-S3-S4). This should cause the plunger to extend outward. If the terminals are connected in reverse order (S4-S3-S2-S1), the motor should rotate in the opposite direction, causing the plunger to retract. This confirms the motor is functioning properly.

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