A Volkswagen Sagitar 1.4TSi car with a mileage of about 110 thousand km in 2011. Users reflect: the cold car is idle and unstable, and sometimes it will stall. At first it was thought that it was an accidental failure, and it didn't repair in time. But recently, the problem has become more and more serious. Inspection and analysis: maintenance personnel detect engine control unit and no failure code is found. No obvious abnormalities were found in engine control parts and tie lines. Measure cylinder pressure, check ignition system and related sensors, and find no abnormalities. Connect the tubing adapter to measure the fuel pressure, normal. Read the coolant temperature, control unit supply voltage and lube oil pressure data are normal. After cleaning the throttle body, idle speed control valve and injector, the oxygen sensor signal is measured by oscilloscope at idle speed. The voltage varies from 0.4 to 0.6 V, the rate of change is 12 times / min, and it is normal. Check the fuel injection correction, and it is normal. Start the car after a night's stop, and then shake the control wiring harness of the engine in the cold vehicle condition. When the wiring harness of the air flowmeter is swaying, the engine idling fluctuates seriously, and it soon flameout. The whole process lasted about 3 to 5S. to disassemble the air flowmeter, and it was found that there was an oil film attached to the sensitive element. Further examination revealed that there was a large amount of grease stain in the intake hose. Judging from experience, the grease stain may come from the lubrication line of the turbocharger. But when pulling out the crankcase ventilation pipe, it found that there was a lot of grease stain. Immediately pull out the dipstick inspection, found that the car lubrication oil quantity is too much. It is considered that the oil and gas separation device in the crankcase ventilation system can not separate the oil mist completely because of the overabundance of the splash lubricating oil when the crankshaft rotates, which is the reason why the lubricating oil enters the engine intake system. In addition, due to the greater drills of the lubricating oil in the cold car, the multiple lubricating oil makes the turning resistance of the crankshaft greater than the design value, which leads to the fluctuation of the idle speed and even the extinguishing. Troubleshooting: release excess lubricating oil, clean up intake system, troubleshooting trial run.