The EGR valve helps your car more efficiently and completely burn fuel by recirculating a portion of your exhaust and running it through the combustion process again. This results in a cooler, more complete burn of the fuel which decreases you car's noxious emissions by prohibiting the formation of some harmful gases. Rough idle and poor acceleration can be caused by a faulty EGR valve. If it was mine, I'd replace the EGR valve with a new one. That engine was not designed to run without one.