A Anhui Jiang Huai Automobile Corp, produced by the Anhui Jiang Huai Automobile Corp, was produced in April 2012. The model number is HFC7150M 1 F, the engine is 4GB2, 1.5L, and 26 thousand km. According to the driver's reflection, the engine's idle speed is unstable after the car starts normally, and when the hot car starts, it needs to increase the throttle or stall easily. Commissioning inspection: after receiving the vehicle, confirm the fault of the vehicle. When the ignition switch is placed in the "ON" position, the emission control indicator light, the engine control device indicator light is lit, the engine is extinguished after starting the engine, and the other warning lights work normally. During cold start, the engine tachometer pointer drops to 2000r/min after a slow descent, and the engine has a larger voice. After starting, the steering wheel has jitter, the engine tachometer pointer has no obvious swing, and the engine can obviously hear the fluctuation of engine noise. As the temperature of the engine rises, the sound of the engine decreases. When stepping on the accelerator pedal, the engine tachometer pointer decreases obviously before rising, and the pointer decreases greatly. Cold car road test, low speed gear, especially 1 block, 2 block acceleration and deceleration oil recovery, obvious setback. When the hot car starts, it is necessary to increase the throttle to start smoothly. Open the engine room for routine inspection. Because the car has not long service life, and the driving mileage is less, the engine bin is clean and tidy, the connection of various pipelines is normal and no breakage, no serious oil leakage marks are found, and the wiring harness of the electronic control system is reliable. There is no maintenance record for engine oil and oil filter. Fault analysis: 1.4GB2 engine idle speed control principle 4GB2 engine is the 1.5L VVT small displacement engine developed by Jiang Huai Automobile Corp in recent years, straight line 4 cylinder, double top camshaft, 16 valve, electronic throttle, timing chain drive, multi point electric injection system, independent point fire, compression ratio 10.5, maximum power 83kW, most Large torque 146N.M. The components of electronic control system are mainly composed of 3 parts. The first part is mainly ECU. The second part is the sensor, including the intake pressure and temperature sensor, the engine coolant temperature sensor, the throttle position sensor, the acceleration pedal position sensor, the crankshaft position sensor, the camshaft position sensor, the heating oxygen sensor, the detonation sensor, the speed sensor. The third part is the actuator, mainly: electronic throttle body, fuel injector, carbon tank electromagnetic valve, ignition coil, variable inlet valve timing oil pressure regulating valve, fuel pump relay, air conditioning relay and so on. The 4GB2 engine idle speed control mode is as follows: according to the basic characteristics of the intake control mode at idle speed, it is generally divided into 2 types: the first is to control the idle speed bypass air passage section size as the basic characteristic, the idle air flow is regulated by the bypass air passage control mode; the second kind is the direct control section. The valve opening is a basic feature, and throttle direct control mode is used to regulate idle air flow. The second types of 4GB2 engines are used in Jianghuai. At idling, the engine ECU determines the speed of the target according to the signals sent by various sensors and switches, and then determines the required control according to the difference between the target speed and the actual engine speed. Finally, the instruction is sent to the electronic throttle to reduce or increase the intake. 2. analysis of the cause of failure after test and analysis of the 4GB2 engine system, it is found that the cause of the engine's idle speed may be caused by 2 aspects: (1) sensor faults, such as valve position sensor, engine coolant temperature sensor, intake pressure and temperature sensor, etc. The fuel injector has poor atomization, drip leakage, poor spark plug ignition reliability, and electronic throttle fault. Troubleshooting: in order to better troubleshoot, the car was put out overnight and detected on the morning of the second day, when the ambient temperature was about 10~15 degrees Celsius. Confirm that the ignition switch is in "LOCK" position and connect the diagnostic plug of the Tong Tong DS708 fault diagnosis system to the vehicle fault diagnosis socket. Open the diagnostic switch, select the "home-made car" Jianghuai V3.0, and turn the ignition key to the "ON" position at the interface of the fault diagnosis instrument. Select "car diagnosis", enter the RS4GB2 engine electronic control system, read the current fault code and historical fault code, all show "the system is normal, no detection of fault code." After exit, select all data flow options in the dynamic data stream. When not started, the coolant temperature is 10 degrees, and the inlet temperature is 11 degrees, which is close to the ambient temperature. After starting, the temperature of the coolant rises gradually, and the inlet temperature is approximately equal to the temperature in the engine compartment, indicating that the temperature sensor and the intake temperature sensor work normally. The absolute pressure of the intake manifold, the sampling value of the intake manifold, the position of the throttle position sensor, the B/D of the relative throttle position and the control of the throttle are changed, which indicates that the absolute pressure sensor and the throttle position sensor of the intake manifold are working normally. Stop stepping on the accelerator pedal, careful observation found that the engine idle speed change range is larger, the minimum and maximum speed difference is more than 50r/min, data flow project "ETC show throttle position" change range, suddenly high and low. Next, an action test was carried out. 4 injectors were opened / closed, ignition advance / delay, and no abnormalities were found. The engine idling control adopts the throttle direct motion. As shown in Figure 1, the throttle position sensor value is changing, indicating that the opening of the electronic throttle is in a large and small change, and the data flow is read again, showing the "idle speed error" value of 112911.07r/min, and the electronic throttle fault is doubted. Turn off the ignition switch and remove the electronic throttle according to the maintenance manual. It is observed that the throttle is dirty, the inner wall behind the blade is yellow, and the finger touch is found to be black on the finger. Try to thoroughly clean the throttle with carburetor cleaner, wipe it with toilet paper and press the throttle blade with your fingers without obvious jerky feeling. The inner wall is the soil yellow indicating that there is unfiltered air in front of the throttle, because the loosening of the connection between the throttle and the intake pipe and the breakage of the intake pipe are not found in disassembly, so the air filter is removed and the filter core is clean. This is the exception. The car runs in the northwestern region for a long time. In winter and spring, there are more sand and dust weather and more dust in the air. After 5 months of the normal filter core, it should be dirty, and then it is found that dust is found at the edge of the upper surface of the filter core, and there is a large gap between the filter core and the outer shell edge of the air filter, as shown in Figure 2. The size of the filter core is too small to make the air filter into the rear air inlet without filtering, which makes the impurities in the throttle body accumulate too much, which affects the rotation of the electronic throttle blade at idle speed. Replace the proper air filter core, check the installation without error, the idle speed is normal, the steering wheel is not jitter, the sound of the engine outside the car is normal, the low speed stop refueling and oil recovery when the car is in test. Maintenance summary: when communicating with the driver, it was learned that the engine air filter element was purchased and installed by the driver 5 months ago. In recent years, China's automobile sales and holdings have risen sharply, but the 4S shop spare parts costs have not decreased significantly. Nowadays, because of the convenience of online shopping and the increase in the number of auto parts sales stores in urban areas, more and more people choose to buy their own spare parts to replace them. In this way, the owners should be reminded to pay attention to the specifications and quality when choosing the spare parts, so as to avoid the damage to the vehicles.