What are the symptoms of a faulty exhaust check valve?

[NoahRose]

Symptoms of a faulty exhaust check valve include extremely unstable idle speed or even stalling, flashing malfunction indicator light, failure to meet annual emission inspection standards, burning engine oil, and blue exhaust smoke. When the exhaust check valve fails, it cannot control the amount of exhaust gas recirculation. Excessive exhaust gas participating in recirculation will affect the concentration of the engine's air-fuel mixture and combustion, leading to symptoms such as illuminated engine warning light, difficulty starting, engine shaking, unstable idle speed, weak acceleration, and failure to meet emission standards. A damaged exhaust valve will affect engine performance, especially during idle, low speed, light load, and cold engine conditions, where recirculated exhaust gas will significantly impact engine operation. The function of the exhaust check valve is to allow high-pressure air to flow unidirectionally to the oil-gas separator, which recirculates the exhaust gas, allowing some of the vehicle's exhaust to re-enter the cylinder for further combustion, thereby reducing the combustion temperature in the cylinder and lowering the NOX content in the exhaust.