Quote:
The EGR valve helps your car more efficiently and completely burn fuel by recirculating a portion of your exhaust and running it through the combustion process again. This results in a cooler, more complete burn of the fuel which decreases you car's noxious emissions by prohibiting the formation of some harmful gases.
And:
The EGR valve, or Exhaust Gas Recirculation valve, is a vacuum controlled valve which allows a specific amount of your exhaust back into the intake manifold. This exhaust mixes with the intake air and actually cools the combustion process. Cooler is always better inside your engine. The exhaust your EGR valve recirculates also prevents the formation of Nitrogen related gases. These are referred to as NOX emissions, and are a common cause for failing emissions testing. Unfortunately, your EGR valve can get stuck, causing NOX gases to build up. You'll know if your EGR valve is stuck or malfunctioning because your car will experience symptoms like rough idle and bucking on accelertaion.
So directs exhaust gas back into the engine which is not really good when the engine needs clean air. If you un-plug it or totally blank it off your engine management light (EML) will come on, although this can be switched off via a Vagcom link. What most folks do is buy a blanking plate with a small hole (or drill one themselves) which allows a small amount of gas through to fool the sensor and keep the light off.
Most people agree the car runs better with the EGR blanked but a few have reported excess smoking under hard throttle, so its a grey area really and you kinda pay your money and take your choice. Its on my list of "do's" now mine is out of warrenty along with de-cating the exhaust at some futre point in time.
Hope that helps
