The EGR is (Exhaust Gas Recirculation). It takes unburnt exhaust gases and puts them back through the cumbustion cycle. If you are not going to take your car through emissions checks, you probably don't need to put the EGR valve back on. The EGR controls the NOX emissions (oxides of nitrogen). If you have a faulty EGR valve or no EGR valve, this causes a rise in the NOX emissions. But again, if you do not have to go through emissions control checks or your emissions controls do not inspect for NOX, you probably don't need the EGR valve. This is a short explaination of the EGR. Hope this helps.