Idle speed problem. I can't adjust well.

Engine idling instability is one of the common faults in automobile use. Although most cars now have fault self-diagnosis systems, there will be cases where the self-diagnosis systems with fault surfaces display normal codes or codes unrelated to faults. This is usually caused by actuator failure or traditional mechanical failure that is not directly controlled by the electronic control unit (ECU). The following lists the causes of Chang Xiong's failure in this case and its diagnosis and elimination methods. 1. Failure analysis of idle switch not closed: When idle contact is disconnected, ECU determines that the engine is in partial load state. At this time, ECU determines the fuel injection quantity according to the air flow meter and crankshaft speed signal. At this time, the engine is idling, and the intake air is less, which leads to the mixture being too rich and the speed increasing. When ECU receives the "rich mixture" signal fed back by oxygen sensor, it reduces the fuel injection amount and increases the opening of idle control valve, resulting in the rich mixture. Reduce the rotation speed. When the ECU receives the signal of "the mixture is too lean" fed back by the oxygen sensor, it increases the fuel injection amount, reduces the opening of the idle control valve, and makes the mixture too rich, thus increasing the speed. Repeatedly idling the engine, turning on the air conditioner, turning on the steering wheel and turning on the headlights will increase the load of the engine. In order to prevent the engine from stalling due to increased load. The ECU will increase the fuel injection quantity to maintain the stable operation of the engine. When the idle contact is disconnected, ECU thinks that the engine is not in idle state, and the fuel injection quantity will increase slightly, so the speed will not increase. Diagnostic method: Turn on the air conditioner and turn the steering wheel when idling. The engine speed does not increase, which can prove this fault. Troubleshooting: Adjust, repair or replace the throttle position sensor. 2. Failure analysis of idle speed control valve (ISC): The electronically controlled idle speed control valve ensures the correct idle speed of EFI engine. ECU adjusts the idle speed control valve according to engine speed, temperature, throttle switch and air conditioner signals. When the idle speed is lower than the set speed, the computer instructs the idle speed control valve to open the air intake bypass channel or directly or directly increase the throttle opening, thereby increasing the air intake and improving the engine idle speed. When the idle speed is higher than the set speed, the computer will instruct the idle speed control valve to close the bypass passage to minimize the intake air and reduce the engine speed. Due to oil pollution and carbon deposition, the idle speed control valve is slow or stuck, and the throttle valve is poorly closed. , so that ECU can not correctly adjust the engine idle speed, resulting in unstable idle speed. Diagnostic method: Check the starting sound of the idle control valve. If there is no starting sound, the idle control valve is faulty. Troubleshooting: Clean or replace the idle speed control valve, and set the idle speed with a special decoder. 3. Fault analysis of air leakage in intake pipe: According to the principle of engine idle stability control, under normal circumstances, the opening of idle control valve strictly follows a certain functional relationship with the air intake, that is, the opening of idle control valve increases, and the air intake also increases accordingly. When the intake pipe leaks, the intake air volume and the opening of the idle control valve will not strictly follow the original functional relationship, that is, the intake air volume suddenly changes with the change of the idle control valve, and the air flowmeter cannot measure the real intake air volume, which leads to the inaccurate control of the intake air volume by ECU and the unstable idle speed of the engine. Diagnosis method: If you hear the smell of air leakage in the intake pipe, it proves that the air intake system is leaking.