The Exhaust Gas Recirculation valve is on top/side of the engine near the alternator. The powertrain computer controls the operation of the valve to allow burned exhaust gasses back into the combustion chamber to re-burn them lowering pollutants. If the computer flags the system as not working correctly it is likely the valve has failed or the exhaust gas passages in the cylinder head or manifold are carboned up and restricted. Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info. and get an online repair manual subscription.