How to Tell if Your EGR Valve Needs to be Cleaned or Replaced
EGR stands for "exhaust gas recirculation". The EGR valve controls the flow of exhaust gases into the intake manifold where they are fed back into the engine to be burned again. Exhaust gasses are fed back into the engine because research has shown that exhaust gases combined with the fuel/air mixture reduces nitrogen oxides (the pollutants that cause smog) and increases the overall efficiency of the combustion process.
So why is there a valve, if exhaust gases help combustion, why not release them into the engine all the time? Under certain circumstances, such as when idling, the fuel and air must be very accurately controlled for the engine to run smoothly. During these periods the presence of exhaust gases would upset this delicate balance and therefore a means of interrupting them must be implemented.
This is the function of the EGR valve. Under conditions when exhaust gases can help the combustion process, it opens and allows the gases to enter the intake manifold. When exhaust would interfere with the smooth operation of the engine, it closes. On modern cars, determining when to open and close the EGR valve is the responsibility of the engine computer.
Most modern car computers monitor many systems and the "check engine" light will illuminate to notify the driver if there is a problem with the EGR valve. At this time it is a good idea to query the computer with a scan tool to determine the exact trouble. If the EGR valve is malfunctioning, an EGR, DTC (diagnostic trouble code) will be generated by the computer.
If the "check engine" light does not illuminate or your car does not have a service light, you can still use your mechanical ability to determine if the EGR valve is working. There are two possible malfunctions of this valve. It is either not opening when it should or not closing when it should.
If the valve does not open, you will notice a small reduction in horsepower. The engine may knock or "ping" under acceleration. It may run a little hotter and seem to labor under load. You may also notice a slight increase in fuel useage. Again, each of these symptoms can have other causes so you must test the valve itself to determine if it is the problem.
If the valve does not close, the engine will idle rough or stall completely when you remove your foot from the accelerator. It may also hesitate when you try to accelerate. These are the same symptoms as a vacuum leak so don't assume the EGR valve is at fault. You must test it.
Testing an EGR valve to see if it is malfunctioning.
Locate and remove the valve from the engine. This is usually accomplished by removing two bolts from the manifold and a vacuum hose from the valve's diaphragm housing. Be careful, exhaust systems get very hot quickly and stay hot for a long time. Once it is removed, inspect it closely. If it is damaged, dented, or parts of it are broken or loose, replace it.
Next, inspect it for carbon build up. Cars used for short, in town trips are notorious for this. Clean the carbon out of the air passages as much as possible. Carbon can not only plug the valve and keep it from opening, it can also make it stick and prevent closing. Check the openings in the manifold for carbon also and clean as necessary. Use a tool or spray cleaner to remove as much carbon as possible. Do not damage the gasket or metal surfaces. If you do, replace the valve or gasket as necessary.
Most of the time, this will correct the malfunction. If you want to do further testing, connect a vacuum pump to the diaphragm housing and apply a vacuum. The valve should hold the vacuum without leaking. If it does not, replace it. As you apply the vacuum, watch for the valve to open. If it does not, it needs more cleaning or replacement.
Once the valve is cleaned or you have a new one, install it on the engine in the reverse order of its removal. If the computer generated an error code, reset it, and you should be well on your way to some trouble free driving.