The mileage is about 160 thousand km, with the imported 2.5 L 2TR engine and FK8 CVT transmission in 2010 imported Reno Leo sports utility vehicle. User response: there is a phenomenon of vehicle idle speed jitter, acceleration inability, and engine fault alarm lights. Inspection analysis: after the car, the author found that the vehicle runs smoothly, and the speed of the engine can reach about 6000 r/min after the landing gear is stepped on the accelerator pedal, which is in line with the normal standard. So the author connected the CLIP fault diagnosis instrument to detect the engine control system of the vehicle, and found the fault code of "DF986 mixture dilute". Through the previous maintenance experience, I think that compared to the normal vehicle air fuel ratio, the mixed ratio of the fault vehicle is seriously maladjusted, that is to say, the oil is less than the normal condition, and the oil less need to consider the following 4 aspects. (1) the measurement misalignment of the signal misalignment air flowmeter will result in the decrease of the actual fuel supply; the signal of the water temperature sensor and the signal of the oxygen sensor will lead to the decrease of the injection pulse width and the decrease of the oil supply. (2) inadequate fuel pressure includes: insufficient fuel pump pressure; fuel injector blockage; fuel pipeline due to external force deformation. (3) if the air leakage at the rear of the air flow meter, the excess air will cause the increase of the actual air flow into the engine cylinder, which will cause the mixed gas to be thinner, and the air leakage of the air intake pipe and the exhaust pipe will lead to the inaccurate detection of the air fuel ratio sensor, which is mistaken for the mixture gas concentration to the engine control unit. Convey information on reducing fuel injection. (4) the failure of the engine control unit requires replacement of the engine control unit and matching or adaptation after replacement. After recording the fault information, the CLIP fault diagnosis instrument is used to observe the current data of the fault vehicle. The long-term fuel correction for the defective vehicle is 139, while the normal range is 75~133. The short-term fuel correction is 125, while the normal range is 75~125 (Figure 1). This indicates that the engine control unit wants to adjust the air fuel ratio to the normal range when the gas mixture is deviated from the normal range, but the engine control unit has been unable to adjust when the engine control unit has been adjusted to the limit value. At this time, the engine fault alarm light is lit by the trigger principle of the two stroke logic. After the fault code is cleared, the CLIP fault diagnosis instrument is connected to the road test. When the speed exceeds 20 km, the fault vehicle appears to break the car. At this time the vehicle accelerates and the speed of the vehicle is very slow. There was even a flameout on the way back to the store. At this time, the data flow is observed by the CLIP fault diagnosis instrument, and it is found that the measurement value of the long-term fuel correction is increasing gradually, and the engine fault alarm light is lit, and then the fault code is found to be the same as before. The author continued to observe the sensitivity of the data flow to air-fuel ratio sensor, and found that it was in accordance with the standard from 2.1 to 2.2 V. So the maintenance personnel continue to check the leakage of the engine outside the phenomenon, in the spray carburetor cleaning agent at the same time to observe the engine speed changes, no abnormal. At this point, the engine is like being pulled out of a vacuum tube, occasionally drastically jitter, occasionally jitter even as if it will be flameout, but it does not take long to restore the state. Why is the engine running abnormal after that long time? Is it related to engine temperature? Then the engine was cooled and the engine was cooled again after the engine was cooled. The engine was expected to wait for a while to observe the engine's operation, but the jitter appeared immediately after the engine was started. I think at this time that the engine jitter should have little relationship with the temperature, but why did it not appear when the car was just connected to the car, and now it has such a serious phenomenon? I suddenly realized that the fault occurred after spraying the carburetor cleaning agent. Is there really a leak in the intake system? So the author again checked the contents of the engine with various questions. Through observation, it is found that the data flow of air flowmeter changes rapidly, but after trying to replace the air flowmeter of the same type of vehicle, the fault is still. After checking the fuel system pressure is 360 kPa, and the normal value of 357 kPa, meet the standard. In the process of overhaul, the author hears not a very obvious "hissing" sound, listen carefully to the sound similar to the sound of air leakage. The sound emitted by the malfunction vehicle is different from the sound of the normal vehicle. When the lower crankcase ventilated No. 2 vacuum tube, it was found that the long-term fuel correction in the data stream gradually decreased, and finally returned to normal range. After the fault code is removed, the long-term fuel correction amount will no longer increase, and the engine fault warning lamp will no longer light up. Why does pulling the crankcase ventilation No. 2 vacuum tube have this effect? Is it changing the previous intake mode? Or is the intake surface increased? At this time, the engine is still shaking, but it can obviously feel that the voice of suspected leakage has changed, which proves that this is a breakthrough to eliminate the fault. After lifting the vehicle, I listened carefully to the various parts of the engine. Through continuous listening, it was found that the noise near the shell of the air filter was most obvious. Then check further and find that the pipeline that has just been disassembled to the front of the throttle is not well connected. When you want to deal with it, it is found that the engine will change during the movement of the resonant cavity. It is found that the engine will shake if the resonant cavity is tightly fitted to the engine, and the engine will not shake if the cavity is opened to a certain position to increase the intake area. At this point, the author's thinking is suddenly enlightened, and the malfunction of the vehicle may be caused by insufficient air intake. The air filter was disassembled to check, and it was found that the inlet side of the air filter core had been deformed because of excessive pressure and was tightly attached to the air inlet of the air flow meter. When the air filter is removed, the engine jitter immediately disappears, and there is no "hissing" sound. Troubleshooting: after the replacement of the damaged air filter, the engine no longer jitter, the engine fault alarm lights no longer light, vehicle acceleration becomes powerful and timely. Review summary: the exclusion of the fault left a very deep impression on the author. Usually, the air filter blockage will cause the excessive concentration of the mixture, but the fault vehicle does not reach this level, only affecting the intake volume. Engine intake is blocked, it will get too much air from other intake channels, which will inevitably cause too much gas mixture, engine failure alarm lights lit. The volume of air intake measured by the air flowmeter in this case will also change. The data is not allowed to be transmitted naturally. The intake of air from the air filter and other gaps will inevitably cause abnormal intake noise. All these require careful observation and careful summary by maintenance personnel.