A Honda civic (CIVIC) car with a mileage of about 150 thousand km. User response: the engine fault lamp of the dashboard is intermittently lit when the vehicle is running. Failure analysis: short 2 pin diagnostic two terminals, turn on the ignition switch, observe the flashing condition of the engine fault lights, confirm the fault code is 11. Referring to the data, it is known that the concentration of idle gas mixture is abnormal. Check the intake manifold. The vacuum line is connected well without leakage or blockage. The fuel pressure is measured, the fuel pressure is 250kPa at idle speed, and the fuel pressure reaches 300kPa when accelerating. Replace spark plug, clean fuel injector, throttle body and idle air control valve. After trial run, failure symptom is not improved. Check the exhaust system and find no oxygen sensor and three element catalytic converter. It shows that the mixture of the engine is open loop control and idling mixture ratio regulator (IMA) should be configured. After careful examination, it is found that there is an electric potential regulator on the driver's foot guard plate, which is confirmed to be an idle speed mixing ratio regulator. Remove the 3 wire harness plug of the regulator, open the ignition switch and measure it, confirm that terminal 1 is the grounding wire terminal, the 2 terminal is the signal terminal, and the 3 terminal is the 5V power line terminal. Measure the resistance between the terminals of the idle speed mixing ratio regulator and result in a circuit breaker. The idle speed mixing ratio regulator is replaced and the signal voltage is adjusted to make the idle mixture concentration return to normal. Road test, failure symptoms completely disappeared, maintenance work ended. When the wire of the idling mixer is broken, the signal line voltage is 5V, beyond the standard range, so the engine control module sets the fault code 11 and activates the engine fault light.