Need to pass Emissions, it passes at idle, but at the 25mph test is fails. I'm in the middle of replacing, plugs, wires, dist. cap and button, as well as the air filter. Is there anything else I can do to help my 1990, 190E 2.6 pass?

I've considered replacing the EGR valve also, isn't there a test that can be done to it to test proper operations before I go and replace it?