I am diagnosing a slightly rough idle on an original 1987 442 with 307 engine that has about 3200 miles on it. I noticed the EGR valve doesn't hold a vacuum. I found a NOS one and that didn't either. I ordered what was an off-shore replacement from the local parts store and that one didn't either. Is it possible that the diaphragm has a controlled leak? The knowledgeable 50 something parts guy remembers something about EGRs that wouldn't hold a vacuum. Does anybody know anything about this and where there is information to substantiate it if true?