Audi a6l, idling at 2: 04, the mixture is too rich! What caused it?

Too rich mixture: When idling, the engine load decreases, the throttle opening decreases and the air intake decreases. At this time, the intake pipe is in a vacuum state due to the smaller throttle opening, and the exhaust gas will be sucked back into the intake pipe when exhausting, resulting in further reduction of oxygen intake in the intake pipe. At this time, if the fuel injection is too concentrated, the air-fuel ratio will be greatly reduced, that is, the proportion of gasoline is too high, then oxygen will be extremely scarce, resulting in very low combustion efficiency and poor economy. It is conceivable that the products will mainly be C, CH, CO and nitrogen oxides, which are neither environmentally friendly nor fuel-consuming, and will also cause the cylinder and spark plug to fail to work normally due to carbon deposition.