P0300 Code

[My Sons Explorer]

Question, on my sons 2002 Explorer we are down to a couple of codes, P0300 and P0316 misfire codes.
When I pull off the plug wires at either the plug or the E Coil I get a good spark but the engine doesn't change, still runs the same. We've checked for vac leaks and can't find any. It starts up really good, runs great on the hi-way, but when at idle it runs a little rough, what could be the issue

Thanks