A Volvo S80 with a mileage of over 340 thousand km, an engine of B5254T2 and a transmission of AW50/51. Customers reflected that after the vehicle was lent, the engine kept high idle speed after coming back. Therefore, Chen diagnosis: when the vehicle arrives at the store, the car is tested, the engine keeps high idle speed, keeps at 1400r/min or so, and the phenomenon is verified. The connection diagnostics VIDA reads the fault code and displays the throttle valve malfunction. There are several reasons for this failure: (1) the throttle is dirty. (2) the throttle of the throttle is damaged. (3) there is a problem with the throttle harness. (4) damage to the engine (ECM). First, remove the throttle check and find the special dirty. After cleaning the throttle, read the trouble code with the diagnostic instrument, and still report the throttle valve malfunction. Then a multimeter is used to measure the resistance on the throttle. The resistance value of #1- 4 is 1.4 ohm, the standard is 1.2 to 3.5 ohm. The value of #2-#3 is 1368 omega (standard 1000~1500 omega). #2-#6 is about 820 Omega when the throttle is closed. It is about 1580 Omega at the full opening of the throttle. #2-#5 is about 1480 Omega when the throttle is closed. It is about 500 Omega at the full opening of the throttle. Results the measurement is within the normal range, which can eliminate the above two possible reasons. The circuit diagram of the throttle is found from the diagnostic instrument, and the line is measured: whether the line between the throttle plug and the engine control module (ECM) is measured. The results show that all six wires are connected, indicating that there is no problem with the route. Next, the voltage terminal of the multimeter is used to measure the terminal 3 of the throttle plug. The 5V voltage is normal and the voltage is normal. Then the black watch of the multimeter is connected to the end of No. 2, and there is still a 5V voltage, which indicates that the iron is also normal. Insert the throttle plug on the throttle and put a pin on the wire harness of terminal 5 and terminal 6. The ignition key opens the II gear, slowly steps down the accelerator pedal, and the 5 and 6 terminals should have voltage changes. Terminal 6 is throttle unit signal potentiometer 1, voltage increases with the increase of throttle position, the voltage will vary from 0.4 to 4V, and terminal 5 is opposite. The measured voltage changed normally. The power supply and the iron on the plug of the throttle are all normal. Terminal 1 and terminal 4 are pulse signals, and multimeter can not measure it. ECM module is generally not easy to damage, so it is generally considered no problem. The wiring harness of the throttle is examined carefully. During the inspection, it was found that the wiring harness of the throttle plug was wrapped by tape, as if someone had touched the wiring harness. When the tape is removed, two wire harnesses are entangled directly. It is possible that the two lines increase with the engine temperature and bump, resulting in the increase of the wire harness, resulting in the difference of the signal and the high idle speed of the engine. Troubleshooting: re welding two lines of trial run, the idle speed is normal, the diagnostic instrument reads the trouble code, and there is no throttle valve malfunction, the problem is solved here. Fault summary: throttle angle is usually measured by potentiometer 1. For small angles, the amplified signal is used to get a clearer signal. The engine control module (ECM) also monitors the throttle cell signals on the potentiometer to check and determine that they are credible, and between the lowest and the highest limits, and the signals correspond to the same throttle angle. If there is a difference in the signal, a virtual throttle signal is calculated from the load signal, the engine speed (r/min) and the state of the time (especially the pressure and temperature), and the potentiometer with the closest signal to the calculated throttle angle is then assumed to be correct. When we repair the wiring harness, we must not wind up a few of them. We must firmly weld them.