Most modern vehicles come equipped with an Exhaust Gas Recirculation valve, otherwise known as the EGR valve. The EGR valve is designed to control the amount of nitrous oxide that builds up in your motor by releasing some of the gases back into the motor and venting the rest out.
The "dirt" that causes your EGR valve to become clogged is not the same kind of dirt you find on the ground. The build-up is actually carbon deposits that accumulate inside your EGR valve and harden. When carbon builds up inside your EGR valve, your car will not run properly.
You can check for carbon-build up by removing your EGR valve and inspecting it for hardened clogs or deposits. A clogged EGR valve has several symptoms.
Your EGR valve operates using a vacuum that controls airflow between the intake manifold and the EGR valve itself. If the EGR valve becomes clogged, there is the possibility that your car vacuum may become too strong and open the EGR valve completely, causing your engine to stall.
When your EGR valve becomes clogged, air and emissions are not able to properly circulate through your engine and your car will not idle properly. A car with a clogged EGR valve has a tendency to cough and sputter while idling.
Knocking or Popping
On rare occasions, a clogged EGR valve cause your engine to make a knocking or popping noise. This can occur when the EGR valve is stuck in the closed position and gases build up in your motor.