EGR recirculates exhaust back into the engine to help control NOx (oxides of nitrogen). These occur at extremely high combustion temperatures(above 2500 degrees if I'm not mistaken). NOx (It is an X because the amount can vary, NO, NO2, ect.) NOx are harmful to the atmosphere. Not only does EGR control NOx, it also CONTROLS knock by diluting the air/fuel mixture with inert exhaust gas (exhaust gas will not burn, thus lowering exhaust gas temperatures). EGR has a "leaning" effect when it is purged into the cylinder, which is why it is only purged on mild acceleration and coasting, not at idle or WOT. Keep your EGR, it does nothing but help your gas mileage, keep your engine knock counts lower and mother earth happy.