EGR Valve Symptoms

Updated February 21, 2017

The Exhaust Gas Recirculation (EGR) valve systems, first added to cars in 1973, reduce the formation of NOx gas by vehicles. The process involves allowing a small amount of exhaust into the intake manifold to cool the combustion temperature. This reduces the reaction between nitrogen and oxygen, the two gases that form NOx. Problems with these valves occur when the valve remains either open or closed. As time passes, the technology behind the EGR systems has advanced. The best course of action involves computer diagnostic testing on your system by a mechanic if your vehicle exhibits symptoms of a problem.

Rough Idle

When the car is running but not moving, the engine idle will be rough. This is a sign that the valve is stuck open. During idle, there is no EGR flow into the manifold. The valve remains closed until the engine warms and is working hard. As the load on the engine increases, the combustion temperature starts to rise. This prompts the EGR valve to open and pull exhaust into the intake manifold. If the valve sticks open, the car will idle roughly when the engine is cold.


The engine will make a knocking noise, indicating that the valve is stuck shut. The failure of the valve to open properly causes a build-up of carbon in the exhaust port. The result is a pinging or knocking when the engine runs. This will be especially true during acceleration. Engine knock is a common symptom of a number of problems. Check the engine temperature, the spark plugs, timing specs and octane fuel percentage. If these issues appear within normal range for your car, the next step is to consider the EGR valve.

Hard Starting

The EGR valve remains closed when the engine is cold. As you attempt to start the car, an open valve creates a vacuum leak in the intake manifold and affects ignition. Carbon build-up on the spark plugs may also cause ignition problems. This build-up occurs when the valve is not operating correctly. The car will start, but it will struggle and may take several attempts before the engine cranks.

Failed Emissions Test

NOx emissions contribute to air pollution. It is the job of the EGR valve to control this form of emission. Many states require testing of this valve and the emission produced by a car before the vehicle can be licensed. If your car fails this test, the EGR valve is not doing its job, and your car is releasing toxic emissions into the air.

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About the Author

Writing since 1999, Darla Ferrara is an award-winning author who specializes in health, diet, fitness and computer technology. She has been published in "Mezzo Magazine" and Diet Spotlight, as well as various online magazines. Ferrara studied biology and emergency medical technology at the University of Nebraska and Southeast Community College.