[Pontyhorse]

It is common for the EGR valve to go bad. That can cause rough running and misfire. The EGR valve is pretty easy to replace. A secondary effect is that the port from the intake manifold can become carboned up to the point it is blocked. (They actually make a kit for this problem consisting of a stainless steel tube to be inserted into the port. That will avoid the problem in the future, but the port has to be drilled out a little.) If a new EGR valve doesn't fix it, removing the intake manifold and cleaning out the port might be in order.