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Volkswagen 1.8T sedan. The car OBD warning light alarm, idle speed is unstable, engine jitter is serious. Fault diagnosis: using "VAS5052A" to make a self diagnosis of the vehicle system and find fault codes: 00369, P0171, 000, which means B1 (the cylinder of the first cylinder) mixed steam. The engine is started and the engine data flow is read. It is found that the air flow meter data and the throttle opening are less than normal. At the idle speed of the engine, the air flow is 1.7g/s, and the throttle angle is 1.2%. But under the same working conditions, the air flow rate of the normal vehicle is 2.1 g/s and the throttle angle is 3.9%. According to the test data, the air intake measured by the air flowmeter is less than the actual intake volume, indicating that there may be air leakage. Check all possible air leakage areas of engine intake system, such as intake manifold, turbocharger, intake manifold, etc. Considering that the fuel evaporation and emission control system will also introduce the outside gas that is not directly measured, the fuel evaporation system will be cut off to the pipe of the intake manifold, and the failure is still. For the crankcase ventilation system, the components that may cause failure are the oil and gas separator on the cylinder head (also known as "oil mist separator"). Install the pilot gasoline separator to the vehicle and troubleshooting. Here, I want to introduce the working principle of the crankcase ventilation system. The crankcase gas of the Teng engine is first inhaled to the crude oil gas separator at the bottom of the cylinder block through the passage on the cylinder wall of the lower part of the cylinder block. Through the treatment of the crude oil and gas separator, the oil in the crankcase gas is separated and reflued into the oil sump, and the separated gas is transported to the oil and gas separator at the upper part of the valve chamber through the pre designed special channel in the cylinder. Because the special channel is integrated with the cylinder body, the gas flowing through is always kept at a certain temperature, thereby avoiding condensation of steam at low temperature. After the gas in the special channel reaches the valve chamber cover, it enters the oil and gas separator directly and carries out the second stage separation of oil and gas. In the oil and gas separator, the gas passes through the treatment of the cyclone separator and condenses the oil droplets. The oil is reflued to the oil pan through the special oil channel on the cylinder head, and the gas separated again reaches the pressure regulating valve in the essential oil and gas separator. The pressure regulating valve is used to regulate the flow of gas into the combustion chamber. When the engine works, it keeps a certain degree of vacuum in the crankcase and ensures the good ventilation of the crankcase. The pressure regulating valve is made up of two chambers. The two parts are separated by diaphragms, one chamber leads to the atmosphere, and the other chamber leads to the intake manifold and the oil-gas separator. When the vacuum degree in the intake manifold is increased, the vacuum degree in the crankshaft is also increased. In order to prevent this situation from happening, the pressure regulating valve regulates the size of the gas channel, and the gas flow rate of the pressure regulating valve is controlled in the appropriate range. The gas separator, as shown in Figure 1, shows that the separated gas is adjusted by the pressure regulating valve in the essential oil gas separator, and then through the control of a one-way valve in the essential oil and gas separator (two unidirectional valves in the oil gas separator, used to control the flow of gas to the inlet manifold or the inlet of the turbine pressurer), and eventually into the combustion. Room. The function of this one-way valve is that if the outlet vacuum of the one-way valve is larger, the one-way valve opens the channel, and the gas adjusted by the surge valve can be inhaled to the intake manifold or the inlet of the turbocharger. By understanding the principle of the work, the reason for the failure is that the diaphragm of the oil mist separator is stuck or damaged, which leads to the connection between the atmosphere and the crankcase, causing the additional air to enter the combustor, as the result of the air leakage of the intake manifold, but it is only more difficult to be released from the air leakage. Additional air into the combustion chamber causes the mixture to dilute, resulting in engine idling instability and jitter. Maintenance summary: with the development of automotive electronic control technology, the diagnosis of engine idling instability is becoming more and more complex, and the idling instability of the sedan is exactly the case. For this kind of trouble elimination, we must first familiarise ourselves with the structure and principle of vehicle related system, and then make full use of advanced professional testing instruments. In the maintenance process, we should also pay attention to the operation of the reference manual, so that we can accurately judge and exclude such failures. In a word, as a car maintenance personnel, we should pay attention to the accumulation of experience in the daily work, and summarize the maintenance knowledge and rules, constantly improve their maintenance skills, and provide some useful reference for others. Maintenance review: today's car is an intelligent carrier, such as a person with a doctor, inquiries (the owner of the answer), the quantity of body temperature (oil / machine temperature), blood pressure (voltage), test (f2I, I) Q'1 tail gas), electrocardiogram (waveform), according to the vehicle disease selection project, neither can check insufficient, nor also You can't check too much. The author uses the diagnostic instrument to detect the engine control unit and store the fault code of "00369 mixture too thin". Query data flow, idle air flow 1.7g/s (normal 2.1 g/s), throttle angle 1.2% (normal 3.9%) author analysis, air flow decreased, the throttle angle decreased, then there must be extra air "do not enter." After a check, it is found that the diaphragm of the pressure regulating valve of the oil mist separator is stuck, causing the air to connect with the crankcase, causing extra air to enter the intake manifold. I totally agree with the author's summary of maintenance. I hope all the "automobile doctors" will adopt the practice of this case, and make reasonable inspection, scientific judgement and correct prescriptions.