Dirty or hanging EGR valve. With it not sealing at idle or lower RPMs it acts exactly like a vaccum leak at the intake. Clears right up once RPMs get past 2000-2500 or so.

Might try pulling it and installing a temporary block off plate between it and intake...see if that helps. If it does, pull the assembly for a thorough cleaning/possible replacement.

The part where #3 and #4 plug wires pulled doesnt effect the engine has got me really puzzled though. That would be an indication of something aint just aint right. EGR wont effect just 2 of 4 cylinders.

~Darin <img src="/forums/images/graemlins/baby.gif" alt="" />