Symptom: a Honda Accord CD5 sedan, in the course of the sudden emergence of the engine idling in the 800 ~ 1200r / min fluctuations between the phenomenon. When the engine starts, the engine speed is 1200r / min, which belongs to the idle speed of the engine. At this time, the engine is running smoothly, but after the engine is running for about 5min, the engine speed fluctuates greatly and the engine speedometer is in the range of 800 ~ 1200r / min There is a regular fluctuation, the instrument panel reported on the engine failure indicator does not light.
    Fault analysis and detection: As the vehicle failure occurred in the cold running conditions to the heat engine operating conditions of the transition phase, it should focus on checking the cold idle control system. One of the water-cooled wax-type fast-speed valve is the idle conditions of idle control system, one of the important components. The valve is located below the throttle body, the opening and closing of the same principle with the paraffin thermostat. In other words, the plumbing fast idling valve in the heat engine without air to the rear of the throttle chamber. Remove the large plastic inlet in front of the throttle valve, you can see in the throttle inside the bottom of a diameter of about 12mm hole, the hole is leading to the plumbing fast idling valve intake channel. It is known from the working principle of the plumbing fast idling valve. When the engine is cold, the air flow through the hole is normal. When the engine is dry, the air flow is not normal.
    With the fingers to block the hole, the engine speed is no longer high and low, tachometer pointer display 750r / min, visible fault caused by the cause of the water in the fast-speed valve this part. For the sake of prudence, in turn the plumbing fast idle valve into the cold water and then into the boiling water, the results confirmed that the valve is good.
    Since the valve is good, then where is the problem? At this point can not help but think in the demolition of the valve leading to the thermostat seat of the small water pipe, the small water tube in the coolant temperature is very high and hot, and the temperature difference between the two is also great. So why is the coolant in the small water pipe and the temperature difference between the coolant in the tank? Will this small water pipe block? Actually observed and found that the middle of the small water pipe connected with the water-fast valve is iron, iron pipe was U-shaped, both ends of the rubber tube and respectively with the water-fast fast valve and thermostat connected. Remove the iron pipe, blowing with compressed air, it really does not work. And then use the wire to clear, clean up a lot of gray powder things, it is estimated that the bad antifreeze corrosion of metal debris, pump water pressure when the corrosion of metal debris rushed here.