emission control causing rough idle?

I don't understand why you would not want to simply remove the valve......or better yet, diagnose to verify that the valve is bad and if so replace it. To me, that would be the best option, but that's not what you originally asked. I simply answered your original question. Especially if there are inspections where you live, you might want to consider a proper diagnosis to verify the valve is bad and then replace it. I'm sure if the valve being bad is the cause of your problem the installation of a new one will straighten it right out and then it will be operating as designed and probably still pass inspection.