1) check the coils.
2) either replace the wires or reseat them all and use dielectric grease in all boots (at the coils too).
It's also a wise investement to get yourself a good scantool. I like the AutoXray, but I'm sure there are others that don't cost too much ($3-500 instead of thousands). Beware though, some cheaper scantools don't sample data frequently enough to be very useful.