An EGR, or Exhaust Gas Recirculation valve is a mechanism which is used to reduce NOx (Nitrogen Oxide) emissions from your engine. The EGR valve, as the name suggests, re-circulates exhaust gases so that it acts as a coolant in the combustion chambers. Over time EGR valves begin to deteriorate as they become sticky and eventually seize open or closed. If seized open the engine may idle poorly or even stall. If seized closed the engine will likely operate at increased temperatures under load and may cause an “engine knock”. This is particularly bad for turbocharged vehicles, as the increased exhaust gas temperature can potentially lead to premature failure of the turbocharger as well.