A 2011 Tuca 2.0L, manual gear, the owner calls out of the process of a sudden no idle speed, too high or too low, stop on the roadside dare not open, ask for rescue. When the technician went out, the following were the following questions: 1. idle control valve (motor); 2. air flow sensor or pressure switch; 3. throttle position sensor; 4. engine control unit; 5. oxygen sensor. The tools are 150 pieces of Shida tools, a KT600 fault diagnosis instrument (with OBD II joint and CAN joint), a digital multimeter, a long short screwdriver each, a test lamp, and no trailer rope. After arriving at the scene, it was found that the fault was exactly the same as that described by the owner. A dozen on fire, but no idle speed (seen from tachometer: between 450 and 4000r/min), and the engine fault light is not bright. Using KT600 to connect OBD 11 and CAN respectively, the fault codes are two: throttle position sensor fault and fuel correction value too high. For fear of what the owner had moved, he first deleted the trouble code and then drove the car, and then detected only one fault code: throttle position sensor failure. Because it is a car that is not available for two years, the same phenomenon is still the same. Then the plug of the throttle position sensor is pulled out (let the engine control unit use only the data of the air flow sensor), but I think the idle speed is more unstable. We have to plug in the throttle position sensor and pull the plug of the inlet pressure / temperature sensor (the control unit uses a default temperature of about 20 C and only the throttle position sensor data), which is the same as that of the throttle position sensor. The same is true for the plug of idle motor. This is a weird thing! It is clearly the influence of these things. Is it caused by unstable oil pressure or gasoline quality? For the latter problem, immediately with the owner confirmation, its oil in Dongguan, Guangdong, the quality is guaranteed (all Dongguan oil station's gasoline is the four standard of Guangdong Province, the four standard), there should be no big problem to ah, and the owner of the car hundreds of kilometers open no problem, there is no reason for gasoline to come out of the problem at this time. No way! You have to look at the data stream. Because of the external rescue, no standard data flow comparison, but still found a few useful data: 1. oxygen sensor data is abnormal, fast speed, oxygen sensor data are about 250mV, the initial show is mixed gas dilute; 2. intake flow rate between 9 to 20gm/s, obviously large (normal about 3), is also The performance of mixed gas dilute; the 3. throttle position sensor voltage is 0.0V, and the control unit is confirmed to be in idle position. At this point, the initial lock is one of two problems: 1. fuel pressure instability; 2. idle motor failure. If the fuel pressure is unstable, it can not be measured directly under the condition of insufficient road rescue equipment at that time. Only after the trouble of idle motor is excluded, it can be deduced as the fuel pressure problem. Then open the key to the ON gear, pull the idle motor plug, with the long screwdriver top on the idle motor plug plug, the top in the ear, no detection of the idle motor action signs, and the normal idle motor in the open key will move. In order to confirm that there is a problem with it, remove the idle motor (connect the plug), one person switch key from OFF to ON, try three or four times, idle motor has no action. The problem was initially found. But because there is no trailer rope, there is something wrong with getting the car back. The options are: 1. unplug the idle motor plug line, the idle motor to the completely closed position, back, adjust the throttle rope tight to the position that can be 1500r/min, this will report failure, but still can open 2 back to the factory. 2. use some kind of sealed material (such as plastic film, etc.) to completely seal the intake of the idle motor, and then pinhole a few small holes (first one, the intake is not enough and one more, and so on) until the idling speed is about 750r/min, no more holes, no plug, a temporary mechanical idling valve. . When you are preparing for one of these two methods, it is found that the idle motor can turn on the opening with a small screwdriver (such as the white part of the red frame shown in Figure 1, the idle motor is closed in the middle first, and the two sides are slowly closed). So carefully rotate it with a screwdriver until a very small angle. The plug line was not installed and loaded back to the trial run. The idle speed can be stable around 750r/min. So, slowly driving the car back to the factory (about 20km from the factory, saving the trailer for the guests). After returning to the factory, more and more wrong, why the mid - gear in 2011, the diagnosis system even the idle motor failure can not be diagnosed, only reported a throttle position sensor fault? Is KT600 not accurate enough? With sceptical psychology, the following results are obtained with X431 (upgrades to the latest data). The following results are obtained: the P0506 idle speed control system's speed expectation is too low; the P0170 fuel correction value fault (BANK1, 1); the P0507 idle speed control system is too high. X431 is more accurate than KT600, or because there is no idle motor position feedback signal in the idling motor, the control unit has given enough open and close signals (from the maximum to the smallest), because of stagnation, idle idle speed, so the throttle position sensor fault. Replace the throttle, troubleshooting. Fault summary: 1. do not fully believe in the report of the fault diagnosis instrument, often one by one according to the related parts of the fault code or all the reasons causing such fault, from easy to difficult; 2. each fault diagnosis instrument has advantages and disadvantages, each factory should be prepared for two or more than two different conditions. Type of fault diagnosis instrument; 3. according to the working principle of a part, moving the brain, temporarily doing some emergency measures or simple replacement equipment, many times to save a lot of trouble.