A 1.8L displacement, AT transmission 2010 Roewe 550 cars. When the owner stated that he had bought a used car from Nanning, it appeared an idling condition on the road and came to the factory for overhaul. The actual situation is: when the idle speed is unstable, the acceleration is normal. During the trial run, it is found that the brake vacuum assist decreases obviously and the brake is hard. Using the KT600 diagnostic instrument, the following fault codes are found: P0700 TCU requests bright MIL lights, P0012 intake camshaft position delay; P0017 exhaust camshaft position jump; P0079 exhaust VVT circuit to ground short circuit or circuit breakage; P0113 intake temperature sensor short circuit to power supply; P0026 entering gas convex axle lock position and unreasonable operation. Failure; P0016 intake camshaft position beating; P0300 multi cylinder fire; P0303 3 cylinder fire; P0304 4 cylinder fire. Ask the owner of the process of failure, the owner said that when the car in Nanning bought a car because of no fuel oil, fill the oil back to run back, later on the way out of this failure phenomenon, second days to my factory to report. According to the principle from easy to difficult, from simple to complex, we have made the following force case for the fault diagnosis of the car: determine whether a fault caused by a fire of a certain cylinder, exclude or determine the fault of the fuel quality, determine or exclude the VVT (variable valve), change or repair the related sensors or actuators. In the case of multi cylinder fire, 1, 2, 3, 4 cylinder high pressure lines were pulled out in turn. It was found that each cylinder had work and the engine working condition was worse when the injector plug was pulled out of 1 cylinders. The fault of non fuel injection and ignition is preliminarily determined. But poor fuel does cause fire. The multi cylinder misfire can cause air intake and exhaust camshaft failures. Then the fuel in the tank was extracted, and the three or four people present agreed that the smell of gasoline was lighter than usual, and that it was a problem of fuel quality, so it took out all the oil in the tank (the car owner's No. 93 gasoline), and added 150 yuan of quality 97 fuel, and removed the fuel filter under the chassis. It is found that the oil poured out of the fuel filter is dirty. After replacing the fuel filter, remove the trouble code and fire again, and find that there is no fundamental improvement in the fault. Again, the spark plug and the injector check, the spark plug shows the constant combustion; the injector is tested on the test machine and found that the fuel injection is very balanced, no problem, no dripping, no clogging. After repeatedly deleting the fault code and starting the car again, it is found that there are always the following fault codes: P0012 intake camshaft position delay; P0300 multiple cylinder fire; P0301 1 cylinder fire; P0302 2 cylinder fire; P0303 3 cylinder fire; P0304 4 cylinder fire. At this point, the fault appears to be "locked" on the intake camshaft. Is it to change the intake camshaft to drive the solenoid valve, according to the "P0012 intake camshaft position delay"? In order to find out the question, I looked at the data flow carefully, and finally found a noteworthy point, "the current error appears on the ignition coil 1", and the state is "activated" (as shown in Figure 1)! Although the relationship between the camshaft and the intake camshaft is not known, but since the diagnostic instrument has reported a problem, the "activation" state indicates that the tester finds it wrong. So the high pressure line of 2 and 4 cylinders (as shown in Figure 2) is clamped with the insulation tongs, and only the "sudden, sudden, sudden" spark pulsation between the high voltage line and the spark plug is heard and the action sound of the "clapper, clatter" solenoid valve with the high pressure line is raised and lowered. Then, after raising and lowering the fourth cylinder high voltage line several times, the engine running seems to be normal. Next to the master to see the actual speed, found to be stable at around 850r/min. The test car is about 4kim or so. There is no idling instability, and the KT600 diagnosmeter is re entered to see the engine data flow, and the state of "the current error appears on the ignition coil 1" is "unactivated". So, the trouble of the car was "muddle headed" and it was "repaired". After changing oil for 7 days and 1 months, the problem was solved. Fault summary: in my personal opinion, the fault of this car is not "muddle headed" and it is repaired. In retrospect, there is still some reason. First, the intake system of the car (the intake camshaft) should cause the card to be in a certain position because of some reason (the reason for the following reason), causing the incorrect air intake, thus producing the idle idle, which can be deduced from the condition that the car has little power loss (almost as much as the normal car) under the condition of acceleration. To verify side effects and improve speed when braking speed is relatively high, we can verify the inference. Secondly, the action sound of the intake or exhaust solenoid valve "clar, clatter, clatter" in the process of the high pressure line (artificially resulting in the lack of cylinder) in the high pressure line with the insulation pliers (artificially caused by the cylinder) indicates that the car has the corresponding action of air intake or exhaust solenoid valve in the case of fire loss, and then infers that the mountain is the cause of a certain original cause in the course of the long drive. In addition to the poor quality of gasoline), it has been a severe fire, and the inlet / exhaust solenoid valve has a big action in the process of fire loss. Because of the oil pressure and other reasons, it causes the kernel to be in a certain position, thus forming the malfunction of the idle speed. Once again, when the oil of the car is checked, the oil has been lower than the minimum line. After 1 months of changing the oil, the problem has never been reproduced.