The waste gas valve is broken. What is the general reason?

The exhaust gas in the circulating valve is not closed tightly, and the fault light flashes.

The reason for this abnormal phenomenon is that the exhaust gas entering the intake pipe through the circulation valve is the exhaust gas after the cylinder burns when there is an exhaust manifold and a cylinder with exhaust gas in the circulation pipeline working. Because these exhaust gases dilute the mixture at idle speed, all cylinders of the engine are in an abnormal state. However, if the cylinder with exhaust manifold and exhaust gas in the circulating pipeline is unplugged, because the cylinder is not ignited, the exhaust gas enters the intake pipe through the circulating valve at this time, which is the unburned new mixed gas discharged by the cylinder, greatly improving the mixed gas quality of the other three cylinders, and the idle speed of the engine naturally rises instead of falling.