A mileage of about 120 thousand km, chassis type W140, equipped with M104 engine and automatic transmission of Mercedes Benz S320 sedan. Users reflect: after the engine repair operation, the engine idling speed is high, so long as it accelerates, there will be a "flying car" phenomenon. After receiving the car: in the trial run, it was found that the engine speed can only drop to 1000r/min, which is obviously higher than that of the normal idle speed. Step on the accelerator pedal. When the engine speed rises, it falls back to 2500~3000 r/min and fluctuates. Check the acceleration pedal cable, there is no stagnation. Check the intake system, there is no gas leakage. The connection diagnostic instrument is self diagnosed. The engine system has the following fault codes: "P1580, the throttle actuator M33 (electronic throttle M33) has trouble"; "P0115, the coolant temperature sensor B60 has a fault," P0507, idle speed control function failure ". Remove the fault code, test the car, the fault is still. The data flow, the temperature of the coolant temperature and the acceleration of the pedal position are normal; the ignition advance angle is -1 degrees, not normal; the angle of the throttle is 0 degrees, and it is not normal. Check engine condition, idle speed is 1000r/min, high. When the speed of the engine is accelerated, it is found that the engine will take a long time (about 10s) to fall to 1300r/min, the ignition advance angle is 30 degrees, and the throttle angle is 0.3 degrees. Turn off the ignition switch and restart the engine. The ignition advance angle of idle condition changes to -11. It is known from the maintenance experience that there are usually three reasons for idling out of control: one is the damage of the throttle actuator or the bad line connection, the two is the bad signal of the accelerator pedal sensor, and the three is the loss of the initialization data of the engine control module. Judging from the symptoms of the car, the latter two reasons are more likely. The accelerator pedal sensor is found on the left side of the engine compartment, and the sensor can be seen to form a mechanical linkage with the accelerator pedal through a cable. Open the ignition switch, slowly step down the accelerator pedal, and then slowly release the accelerator pedal, at the same time observation of the diagnostic instrument data changes, acceleration pedal sensor signal voltage between 0.35 to 4.27V change, indicating that the accelerator pedal sensor has no problem. We continue to diagnose the engine control module and find that the data of the throttle programming project is "No", which means that the engine control module does not store the initial angle of the electronic throttle. The cause of the failure is found, so the adaptive initialization project of the control module matching menu is selected, and the acceleration pedal sensor and the electronic throttle are initialized according to the prompting information. After completion of the test, the engine idle speed is stable, the acceleration performance is good, and the fault is completely eliminated. Under idle condition, the ignition advance angle standard value is 8~12 degrees, and the throttle opening angle standard value is 1~3 degrees. If the engine control module does not correctly identify the throttle angle, the emergency operation mode control idling will be enabled and the engine speed is stabilized by adjusting the ignition advance angle, thus this case is presented. The cause of the failure may be to unplug the wire harness plug of the electronic throttle in the case of opening the ignition switch, which leads to the loss of the initial angle of the throttle of the engine control module. This kind of fault can only be eliminated by special diagnostic instrument, and it is troublesome to repair it, but if we observe the standard operating rules, this kind of fault can be avoided.