Although regular maintenance of your Mercedes EGR valve is not a common requirement, it still needs to be checked to ensure that the exhaust system of your Mercedes is well functioning and is complying with the emission standards. When the exhaust system of your Mercedes has a defective EGR valve, the engine is seriously at risk. Typical symptoms of a faulty EGR valve include the engine knock, poor gas mileage, reduced performance, and excessive emissions. Your Mercedes EGR valve is the main component in your Mercedes' EGR system. It has a small vessel that opens between the manifold and exhaust for the backflow of a metered amount of exhaust. The backflow lowers the combustion temperature as the formation of nitrogen oxides is regulated. The exhaust is brought back to the combustion chamber because the exhausted air is a lot hotter that the intake air. The emissions of nitrous oxides are produced due to burning of fuel at 2,500 degrees Fahrenheit. EGR valves were introduced in 1972 when emissions were taken seriously. Older vehicles utilized the mechanical engine EGR valves. Most of the modern vehicles have electronic valves that use one or more solenoids or small stepper motor. When the engine is cold and idle, the EGR valve is maintained to be closed. It must open only if the engine has warmed up and is running in part-throttle. When the valve is disconnected, NOX emissions will rise, resulting to detonation. Once the valve fails to close all the way, it will act as a vacuum leak causing a rough idle, hesitation and possible stalling. Our 24-hour online store has a large stock of EGR Valves including the ones for your Mercedes. Check out our parts catalog for an easy EGR valve search. Call us toll free if in case you run into some trouble.