Fault phenomenon: one is equipped with three cylinder electric jet engine Geely, because the car has been hot when it is repaired, so only after the engine is running, the first is the high idle speed. When the speed drops down, it falls too low, then returns to the normal speed, but it can also feel the engine's speed fluctuates occasionally. In addition, according to the owner's reflection: the car also has the trouble of starting cold cars. Troubleshooting and Troubleshooting: first, read the fault code, display the trouble free code, and the system is normal. It is found that the range of injection pulse width is relatively large and varies from 1.7 to 2.1ms. Then the vacuum meter is used to measure the vacuum degree of the intake pipe. The readings of the vacuum table are oscillating near the middle line at 20inHg (about 65kPa), and the amplitude of the swing is 2inHg (about 7kPa). According to experience, the vacuum degree belongs to the normal range. In addition, the fuel consumption of the driver was inquired. The fuel consumption was basically normal and the timing problem of gas distribution could be ruled out. When the fire was correct, the ignition time was detected, and the ignition time was earlier than the normal position (using the electric jet engine of the joint electronic company, the normal idling mark at the front of the observation window, the good) early 10 degrees, adjusting the angle of the distributor, after the normal position, the idle speed became smooth. After reading the data flow, it is found that the change range of the injection pulse width is smaller, changes in 1.7 ~ 1.9ms, and the engine speed is more stable than before. After a few days' trial, the fault is ruled out. Normally, the high pressure fire is sent to the spark plug slightly before the piston reaches the top stop point, because this is the moment when the cylinder pressure is the highest. On the one hand, because of the small gap between the gas and the gasoline molecules, the mixture of air and gasoline is more uniform, and the mixture is easy to ignite; on the other hand, the compression is at the end. The temperature of the cylinder gas is also the highest, and the stable flame core is easily formed around the spark plug, so the accuracy of ignition timing will affect the success rate of ignition. The high pressure fire that is sent to the spark plug has missed the best time to ignition, so it will reduce the success rate of the ignition and show the trouble of the difficult starting of the cold car, which is similar to that of the other causes such as the low cylinder pressure caused by the cylinder leakage. The analysis of idle speed instability of hot cars is that when the car is hot, the number of idle motors gradually decreases. When the idle motor is down to a certain normal position, the computer adjusts the ignition time and the pulse width to complete the idle speed adjustment, in order to maintain the idle speed of the idle speed. Because the ignition timing is not allowed, it affects the work efficiency of the engine and the engine can not run smoothly. The computer only increases the step number of the stepping motor and increases the injection pulse width to maintain the idle speed. This adjustment conceals the essence of the fault, so the phenomenon of the hot car after the fault is better, only the high fluctuation of the idle speed, all kinds of adjustments are not beyond the range of the computer adjustment, so the fault code is not stored. It needs to be explained that, although the location of the distributor is more than 10 degrees, but because the car is equipped with a detonation sensor, the engine can automatically delay the ignition time when the ignition is premature and detonation, so the real ignition of the engine is just a bit early in the idle state and little influence in other working conditions. It does not have much effect on the fuel consumption. The calibration ignition timing is to give the computer a wider automatic adjustment ability, so that the engine can run well in various working conditions and achieve the normal working condition. Table 1 is the comparison of the engine data flow before and after maintenance. From the data in Table 1, we can see that the trouble free vehicle engine operates smoothly and the injection pulse width is narrow. The fault car is unstable at idle speed, high speed and high fluctuation, the injection pulse width is 0.2ms wider than that of the normal car, and the engine load is slightly higher. Compared with the normal car, there are also differences between the corrected gas leakage and the two parameters of auto correction of mixed gas. In addition, the exhaust of the malfunction vehicle is uneven and has impact. All these failures and measurement data have basically returned to normal after maintenance.