【Inspection process】
    First, with V.A.G1551 fault reader detection, display is the problem of air flow meter, but the actual detection of air flow meter normal, replace the new air flow meter after the failure phenomenon remains the same. Second, the measured oxygen sensor signal voltage is generally between 0 ~ 0.3V, and the signal does not change or slow change, about 5 to 10 times / min, the normal situation should be 20 to 30 times / min.
    【Fault Analysis】
    Why is the problem of oxygen sensor, but the fault reader shows the air flow meter is the problem? This is related to the design of the car self-diagnosis system.
    From the air flow meter and oxygen sensor function, there is a close relationship between the two. The air flow meter signal is the basis for the formulation of the air-fuel ratio of the ECU, and the oxygen sensor acts to correct the air-fuel ratio error. Oxygen sensor on the air-fuel ratio correction is limited, generally within ± 10% range, so when the oxygen sensor can be amended beyond the limits of the car's self-diagnosis system that is the air flow meter "metering are not allowed" Fault and memory fault code.
    In addition, the amount of oxygen sensor correction is constantly changing, the main reason for the change is the carbon particles in the exhaust, lead and silicide. In the case we encountered, mostly due to the surface of the oxygen sensor caused by carbon. When these harmful substances are deposited on the oxygen sensor, the exhaust gas is not easy to penetrate the porous ceramic carrier and the electrolyte surface, so that the oxygen sensor signal voltage gradually decreased, ECU air-fuel ratio correction frequency is gradually decreased.
    When the voltage signal from 1.0V down to 0.3V or so, the revised frequency from 20 to 30 times / min down to 10 times / min below the frequency and signal voltage represents the lean mixture, so the ECU control the injector More fuel injection, enrichment mixture, resulting in the engine at idle due to the mixture is too thick and poor combustion, idle instability, increased emissions, serious due to lack of power when the car in the car start, loose throttle when the flame. When the engine into the heavy load, because the ECU control oxygen sensor signal is no longer the air-fuel ratio correction, the engine and transferred to normal work.
    【Maintenance】
    Replace the new oxygen sensor after troubleshooting.
    【Maintenance】
    Oxygen sensor surface dirt (common is coke), the phenomenon of idle instability will occur. After the surface clean up, you can rule out the failure or failure phenomenon was improved.