Fault phenomenon
    A Honda Accord car, start difficult, idle instability, speed up shivering, cold when the phenomenon is more serious. Its engine fault indicator light is always bright.
    Troubleshooting and troubleshooting
    The inspection found that when you do not step on the accelerator pedal to start more difficult to step on the throttle easier to start, but after the start of a lift the engine to turn off the engine. If the engine has been running after the start of the accelerator pedal, after a period of time and then slowly throttle pedal, the engine can also run, but the idle instability, swimming between 450 ~ 650r / min swimming, vacuum in 47 ~ 55kPa change, To 2500r / min above all normal.
    Analysis: This type of failure occurred in many other vehicles, mostly because of the throttle body dirty or idle control valve caused by serious carbon deposition. The main point of failure is that the intake air is limited, because the cold start, the intake air volume is relatively large, although the computer will control the idle control valve to amend, but this requires a process. So many times because of the throttle body dirty or idle control valve coke serious cause such failure. But this failure rarely causes the fault light to light up.
    First, the intake system was inspected and cleaned. Check the results for the intake system of the pipeline connection is intact, no leakage, clogging phenomenon, throttle position sensor and idle control valve work well.
    The engine electronic control system was checked with a fault diagnostic apparatus. Read the fault code for the P0131 - oxygen sensor circuit voltage is too low. Remove the oxygen sensor, the surface is not carbon deposition, measuring the wire connection is reliable, indicating that the oxygen sensor is normal. But the oxygen sensor feedback voltage is always less than 0.45V, indicating that the mixture is too thin. Unplug the water temperature sensor harness connector, connected to a rheostat transferred to 4 ~ 8kΩ (due to the water temperature sensor of a fuel injection control correction signal, the temperature is high to reduce fuel injection, low temperature fuel injection increases, plus a 4 ~ 8kΩ, Increase the fuel injection at 0 ° C) Once again, the oxygen sensor feedback voltage is close to 0.9V, further indicating that the oxygen sensor is normal, but the mixture is too thin.
    The measured fuel pressure is 285 kPa, normal. Remove the fuel injector after the failure is still fault, the fault code is only P0131. Unplug the other sensor test, to read the corresponding fault code, that ECU no problem, is certainly caused by leakage. On the intake system and connected to the vacuum tube one by one inspection or no abnormalities. And EVAP, EGR system to troubleshoot, when unplugging the vacuum tube on the EGR valve, the engine idling up to 1000r / min, vacuum also increased and stabilized at 68kPa.
    Editor's Note: EGR valve through the pipeline to connect the exhaust pipe and the inlet, the vacuum chamber above the vacuum by the EGR control solenoid valve control, EGR control solenoid valve by the ECU control. The ECU controls the degree of vacuum of the EGR control solenoid to control the degree of vacuum above the vacuum chamber of the EGR valve according to the engine speed, air flow, intake pressure, temperature and other signals to control the opening degree of the EGR valve to change the participation cycle Of the amount of exhaust gas. In the upper part of the EGR valve there is a position sensor, its function is to detect the EGR valve opening position, and use the potentiometer to its position into the corresponding voltage signal, feedback to the ECU, as the control of exhaust gas recirculation reference signal. The EGR system does not work at idle conditions.
    After unplugging the EGR valve on the vacuum tube, hand blocked the tube found to have a vacuum suction, under normal circumstances this time there is no vacuum. It is because the vacuum suction causes the exhaust gas to circulate under idling conditions, which causes the mixture to be too thin and unstable. Then unplug the EGR control solenoid valve harness connector and find that the vacuum tube still has a vacuum (EGR control solenoid valve to cut off the EGR valve to the EGR vacuum control valve in the absence of electricity), fully indicating that the EGR control solenoid valve is faulty. Further examination found that the valve is dirty, so with carburetor clear detergent and drip two drops of clean oil, installed after the troubleshooting.