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The mileage is about 160 thousand km, which is equipped with BGC1. 8L turbocharger engine, matching the 01 V5 automatic gearbox in 2007 Volkswagen Passat. The engine is unstable at idle speed. Inspection and analysis: the car fault has been checked by another maintenance personnel, first of all with the maintenance personnel to communicate that the car in the normal driving of the EPC light on the instrument, and the engine is still unstable idle, after the failure, the maintenance personnel checked the fuel pressure, the fuel pressure at idle speed is 4. 0bar; still checked. Check the intake hose, there is no leakage phenomenon; replaced the air flow meter, after examination did not exclude the fault. After starting the engine, the EPC light on the instrument cluster is not lit, and the engine idling is unstable. Then use the vehicle diagnosis to check the fault code in the engine electronic device. After inspection, it is found that there is a fault code - 17705 meaning: the pressure drop of the turbocharger - the throttle connection pressure (static). Recall that the EPC lights were on when the customer failed to respond. Why did there not be a fault code related to EPC in the engine electronic device? For example, the fault code of the throttle. Inquiring to repair the vehicle's repairman, it is true that after the failure, the fault codes of several valves have been found. After clearing the fault code to the throttle, there is no fault code, but the fault code 17705 after starting the engine. According to previous experience of repairing similar faults of the vehicle, preliminary analysis is made that the cause of the fault may be the release of the pressurized air hose. Lift the vehicle and remove the engine guard plate. After checking the turbocharger hose connection is normal, there is no phenomenon of disengagement or abrasion. Again, use the vehicle diagnosmeter into the engine electronic device to see the engine's idling data, and display group 001 data: engine speed: 720 to 840/min engine temperature: 93 degrees short term fuel correction: 25% display group 002 data: engine speed: 720 to 840/min engine load: 32% injection pulse width: 4. 6ms Air flow: about 8.3g/s display group 003: engine speed: 720 ~ 840/min air flow: 8.3g/s throttle opening: 2% to 4.3% display groups 015 and 016 are engine "fire" data, all cylinders have "fire" phenomenon, and the number of "fire" in each cylinder are more than 40 times. As the engine idling is unstable, the data read is also unstable, and the above data are close to the data of engine operation. Through the short-term fuel correction in the above data, it can be seen that the engine mixture is too thin, and the cause of "fire" in all cylinders may be too thin, and all the hoses connected to the intake manifold have not been leaked. When the engine is idle, the hose on the intake manifold is clamped, and the unstable operation of the engine does not show any improvement. This indicates that the reason for the over dilution of the mixture is not due to the leakage of the hose connected to the intake manifold. Then the data of the engine is re analyzed. It is found that the data of the air flow meter does not match the data of the throttle, and the throttle opening of the idle speed is 2% to 4.3%, and the air flow is 8.3g/s at that time. What is the relationship between the above two data and the fault code 17705? The meaning of fault code 17705 is the pressure drop of the turbocharger - throttle connection, since the pressure drop is mentioned in the fault code, the so-called pressure drop is the pressure pressure. The control unit is to obtain the boost pressure through the boost pressure sensor, which is installed on the upper part of the pressurized air cooler. If the air flow rate detected by the air flow meter increases, and the pressure sensor detected by the pressurized pressure sensor does not increase with the intake volume, the control unit considers the pressure drop, and the fault code 17705 is stored. Considering that the plug of the booster pressure sensor is removed, the control unit adopts a fixed value 1400mbar instead. After removing the fault code, starting the engine after the plug is pulled out, the engine speed is higher than the idle speed after starting, and the unstable operation is obviously improved, and the reading fault code discovery 17705 does not appear. This indicates that the control unit does detect the low pressure of the booster air. What causes the supercharging pressure to be too low? The repairman reminiscent of the vehicle reflects that the fuel pressure of the car is 4.0bar at idle speed, and the oil pressure of the car is 3.5 bar at idle speed, and the oil pressure on the vacuum tube on the oil pressure regulator is 4. 0bar. The hydraulic pressure of the car is 4. 0bar, which indicates that the pressure in the intake manifold is too large and the vacuum is reduced. The cause of this failure may be the throttle damage, causing too much pressurized air to enter the intake manifold. When the intake hose on the throttle door is removed, the air valve is pushed by hand, and the gap is too large. The gap between the points is the clearance between the internal gears of the throttle body. Remove the throttle valve and open the cover with sliding contact. It is found that there is a lot of oil in it. After careful examination, the internal gear is damaged. Replace the throttle valve again after failure, and start engine smoothly after idling. Troubleshooting: replace the throttle. Summary and analysis: the data of checking the throttle and air flow meter when removing the fault of the car found that the data of both of the two are inconsistent, the data of the idle speed air flow meter are too large, and the pressure of the fuel oil is found to be high in the intake manifold, and the fault appears in the throttle.