emission control causing rough idle?

Just block the sucker off and call it a day . When EGR is functioning properly , it's a good thing ; but when it starts giving ya fits ya gotta either service it ( it may be plugged with carbon , as will any heat crossover ... not sure if the Slant Six has such a thing ... ) , replace it , or dump it .

If you service it -- and the breather / rest of the PCV system -- and the problem persists , then block it off .