EGR stands for exhaust gas recirculation. The EGR valve will generally make the car run poor at lower speeds or idle, but can effect it anywhere. The valve should not open at idle. Operate at midrange speeds and quit again before wide open throttle. The egr valve is usually located on the intake manifold or head. There is a diaphram in the egr valve. The valve uses manifold vacuum on the diaphram to lift or close a valve allowing exhaust gas to enter the intake manifold. An easy test for the diaphram is to remove the vacuum line that runs to the egr valve. You can normally reach the diaphram area with your finger. Move this opposite from the direction it normally sits at. Then cover the vacuum port located on the egr valve with a plugged hose or your finger. The diaphram should either stay in this other position or slowly move to the normal position. If it won’t hold vacuum and instantly returns to it’s origional position, either a vacuum port is still not plugged or the diaphram is leaking. If it is leaking replace the egr valve. If the egr valve holds vacuum then remove the valve from the manifold.