Maybe you have a sticky valve, or a partially clogged injector. ? I'm not totally sure however a MotorVac made my buddies Blazer run great, and made the rough idle completely disappear.
"Damn the torpedos, four bells full speed ahead"
-1987 300E Smoke Silver
-1997 S320 Black on Black
-Soon To be E55 AMG
-27 foot Grady White Offshore Sportfish.