I have a full size 1990 - 20 GMC Van. It has a very rough idle but is fine once cruising or accelerating. It is my belief that this is a result of the engine's EGR Valve not working correctly and/or a blocked in-line fuel filter (the gas tank sending unit and filter have recently been changed). If someone has had a similar experience or knows how to remedy this condition I would be greatly appreciative of their help! Thank you.