Are your plugs & wires due to be replaced? I would change the wires first. I'm not sure how you tested the wires, but it may not be conclusive, & if one is dead, I would definitely change them all. You mentioned just looking at plugs? That isn't going to guarantee that they are OK. I would do the plugs next. You're not wasting money here if these are things you need to replace anyway.
As I have posted previously, I had a wire die at 1000 miles - heat killed it - it was touching the intake manifold. If any of your wires are touching or too close to the manifold, I would use plastic ties & get them up & away from it. Even if no wires are touching, it's fairly common for Contours to kill wires prematurely from heat.
If new wires and plugs don't solve your problem, I would suspect the coil pack next - then the computer. But I see more coil packs go bad than computers. I believe a bad coil pack can affect just one cylinder. Go here for more info on coil packs (DIS Module):
http://www.babcox.com/editorial/us/us89920.htm And a bad wire can burn up a coil pack.
