I do not have the answers to your questions, but I can relate to your distaste of the crud that is deposited in the intake from the EGR valve. I had the intake off of my 96E300D and I was amazed as to the amount of sludge. Thankfully it had not turned hard as is the case in a gas burner. I could not imagine trying to chisle that stuff off of an aluminumum intake and head. I would suspect that the computer would not throw a code becaule it only reads whether the valve is open or closed. as far as performance I would be curious about that. How many miles do you ahve n your 97, and have you had much trouble with it?

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Keith Schuster
2006 E350 98K miles
2013 Ford Explorer 15K miles