*** UPDATE *** PLEASE SEE THE PDF FILE ATTACHED (POST #4) *** UPDATE *** - All photos were held on Photobucket, but due to a change in their policy, I can no longer direct link them. Please see the new version in PDF format.   I know Tech1e did a little write up on this a few years ago, but i thought id do a bit more of a detailed write up with a few more pictures. With use the engines EGR valve allows soot and gunk to block a feed pipe at the intake manifold. it blocks the EGR flow