emission control causing rough idle?

Yes and when he gets a flash fire from dumping something flammable into a running engine following your advice, won't you just feel good? I never advise anything flammable looking for vacuum leaks. I cannot for the life of me figure out why in the world people do it and they do it all the time. Water in a spary bottle works just as well, if not better with no danger of fire. I have seen a person go to the ER for 2nd degree face burns from an under hood fire and explosion because he was using carburetor cleaner looking for vacuum leaks. I strongly advise against it.