I have the code for the EGR valve on my CEL. Also have a downstream 02 sensor code. I had one for the knock sensor but i replaced it and now no more code for that one. My question is should i just go ahead and replace the EGR? The code went away and came back a couple of times and im not sure if it means the valve needs replaced. I was thinking about cleaning it, but it does look pretty old and rusty. Also i cant find a catalytic converter under my car, and no downstream 02 sensor. There is a wire coming out of the chassy about midway above the exhaust, but looks like it was cut. Do i need to get a new exhaust and cat? The car runs pretty rough and misfires a lot, but is driveable.