My 96 850 with 143K miles has been running roughly intermittently - seems to be correlated with not driving it for several days. Sometimes the engine runs very smooth, when well-warmed up for example, sometimes it's jerky and rough.

A couple of weeks ago it threw a P0304 code - misfire in cylinder #4. I inspected the plugs and wires, and all seemed OK, except the #4 wire was brownish in the long straight region between the plug and the seal. All the other wires were light gray. I reset the code and drove for a while, then it threw the same code, same cylinder again today.

I'm thinking about replacing the wires, cap and rotor, which have ~80K on them. That should overkill this problem, I hope. In the meantime, does anyone have any thoughts about whether this brownish #4 wire is really the cause of the roughness, and if so, whether it points to other issues?

Thanks