If it is pressure check your accumulator bronze coloured metal piece to the lower right of the fuel dist. Make sure it is holding pressure, also check the fuel line pressure coming in to the fuel distributor make sure it is at the spec psi.
Is the rough idle due one particular cylinder, when they changed the plugs was one wet or discoloured compared to the others, try and determine if it is just one cylinder that is causing the problem.
By the way I replaced all my injectors, mounts and seals for $250 in parts and 1.5 hrs of my time. m
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)