Cylinder 3 running rich. Injector? Coil pack?

[ColdCase]

Does cylinder 3 typically run rich on these 1.6l 2004 engines (second cylinder from right)? After it was running rough I replaced plugs, cables, and valve cover gasket (#1 and #3 looked like they had just a little oil contamination, 3 being worse). Got a lot of white smoke on initial startup (but it ran fine). No smoke since.

I cleared the codes but after a couple weeks the check engine light came back with P1781 and then a few days later a few mis-fire codes. I pulled the plugs, 1,2, and 4 look fine, #3 a little carbon. I may be in for an injector, but before I dig in I wanted to check in here.

If it was a cat or coil pack, would you think more of the plugs would show rich? It runs fine, with a little rough idle at times. 80,000 miles on it.