Standard Motor Products VS117 EGR Valve - Compatible with Multiple Vehicle Models - High Performance Exhaust Gas Recirculation Valve - Perfect for Emissions Control & Engine Efficiency Improvement

When you let your foot off the gas, this thing opens the EGR allowing exhaust gasses to replace fuel gasses in the combustion chamber (because you're not needing the power). When it's working wrong you don't get the power. When it's not working you don't gain any mileage. When it's working correctly it sounds slightly like a big truck slowing down. Now you know. You're welcome lol.