At high temperature, the negative pressure of the fuel tank is large, and the idle speed is unstable.

1, idle speed control valve failure: the normal idle speed of the engine is guaranteed by the idle speed control valve (ISC). According to the signals of engine speed, temperature, throttle switch and air conditioner switch, ECU can increase the intake bypass passage of idle speed control valve or directly increase the throttle opening, thus increasing the intake air volume and improving the engine idle speed.

2. The fuel injector leaks oil or is blocked: the fuel cannot be injected according to the instruction of ECU, thus causing the mixture to be too rich or too thin, making individual cylinders work badly and leading to unstable engine idle speed.

3. Exhaust system blockage: When the three-way catalytic converter is partially blocked due to carbon deposition and damage, the exhaust resistance will increase and the negative pressure of the intake pipe will decrease, resulting in poor exhaust and insufficient intake of the engine, poor engine performance and idle vibration, and may also cause ECU to remember the fault code of the air flow sensor.

4.EGR valve opens at idle speed: EGR valve only opens at low engine load. The function of EGR is that part of exhaust gas enters the combustion chamber, which lowers the combustion chamber temperature and reduces Nox emission. However, too much exhaust gas will affect the ignition performance of the mixture, thus affecting the power of the engine, especially when the engine is idling, low speed and light load.