What is an EGR Valve?

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  • Written By: CPW
  • Edited By: Jay Garcia
  • Last Modified Date: 26 November 2018
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An Exhaust Gas Recirculation (EGR) valve is a mechanical component found on automobiles and plays an integral part in the proper functioning of gasoline and diesel-engined cars. It ensures that the car burns its fuel effectively by recirculating the emissions from the exhaust through the car’s combustion system. Properly recirculated fuel results in cooler and fuller burning, along with a reduction in the quantity of harmful gases, especially nitrogen oxide (NO). When NO meets the air, is turned into nitrogen dioxide, which in turn becomes smog when it encounters hydrocarbons. In vehicles where the EGR valve is faulty, the driver commonly finds that acceleration is difficult or that the car experiences rough idling or stalls.

The first EGR valve was installed in cars in 1972. They were originally mechanical, and have been superseded by the more modern and much more sophisticated electronic valves. The latest versions are not only capable of self monitoring, but they periodically create problems for the system to ensure the correct response is produced. On some systems, should system fail or encounter a problem, it will automatically produce a diagnostic trouble code (DTC).

The EGR valve is considered by the motor-manufacturing industry as a "metered intake leak" and was invented to lower the fuel combustion temperature. This component is involved in the combustion process for most of a car’s journey, save for when the car is at either end of its performance capacity: idle or full acceleration.


During full acceleration, the valve is disabled to encourage combustion and fill the combustion chambers, a set of conditions called wide open throttle (WOT). Were it to be invoked during full acceleration, it would inhibit the acceleration by reducing the capacity of the fuel combustion chambers. At the other end of the scale, when the car is idling, it is especially sensitive to the composition of air and fuel in the combustion chamber, and therefore the EGR valve is turned off. Should the component still be in operation when the car is idle, the vehicle is likely to stall or stumble.

Though not recommended, some vehicle owners remove or otherwise disable their EGR valves in the belief that it will improve the vehicles’ performance. A car with a disabled valve will not pass an emissions test, and this process is discouraged by the motoring industry.


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Post 9

@anon163648: Sounds like an EGR valve. I'm 99 percent sure of it.

Post 8

May be the throttle position sensor.

Post 5

@Post 1: You may have an air leak. Check to see if all air vacuum lines are attached. Your choke may be stuck as well.

In addition, mechanical lines to your fuel system may be stuck and not allowing the line to completely close. Trace the line and spray grease on the exposed parts. In addition, something may be obstructing the mechanical parts which will not allow it to move all the way to close.

Post 4

@Post 3: It may be a vacuum leak. A VL can cause cars to idle rough and also can impede fuel intake, causing a misfire. Check to see all of your air lines are connected, and in good shape. A leak/or unattached line can cause an engine to run rough and weird.

When you replaced the EGR valve, did you clean out the exhaust ports? They can become very clogged since exhaust gas runs through them can build up and either partially or completely clog. Before you replaced the EGR Valve, did you do a check to see if the plunger was moving?

Put the car in idle with your foot on the break, and have somebody see if the

valve opens. You want it closed, because the engine needs a strong oxygen level to idle. You may not have had to replace your EGR valve, but have cleaned it and clean out the ports. First check where the valve is attached, and clean it out. Re-install and see if the engine runs fine. If not, you may have to take off your intake manifold and clean the internal ports. (Check web for your particular engine. Look up EGR repair and cleaning.)

Post 3

I have a 97 Mercury cougar and it has no power whatsoever. it revs good in park but won't move in drive. i got it checked by a machine and it said that one and two were leaning and that the egr valve was bad. i then replaced the egr valve and the solenoid and the sensor connected to the solenoid and it has not improved. Can anyone help me, please?

Post 1

I have a 2001 Mercury Sable and the engine light is flashing on and off. When i first start the car in the morning, it idles very high and the rpm are at 3. it may go down to 2, as i continue to drive it. i don't have to put my foot on the gas and it runs 35mph. When i come to a stop it's still idling high and sounds loud. What could this problem be? Sign a female

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