misfire code for #4 & #7 comes and goes

[70ray]

I have a 2001 Mountaineer 5.0 with about 90k on the clock. Tonight when I started it up the engine ran rough. At the tail pipe it sounded like a dead miss. I checked under the hood for loose spark plug wires or a vacuum hose that may have come off. Everything looked okay. I turned off the engine I went inside the house to have dinner. When I came back out to the garage, I started the engine up again and it ran fine???? I let it run for a few minutes and all of a sudden it statred to misfire again. I shut it down and I again looked for wires/vac hoses off or damaged---nothing!!! I went back in the house to warm up abit (it is 12* here tonight). After I got warmed up I went back out to the garage again and restarted the engine. It ran fine, but now the CEL was on. So I drove the car down to our local Auto Advantage to have them pull codes. He found a code for #4 & #7 misfire and a O2 sensor code (I think he said it was a LEAN code) ---sorry I didn't write down the code numbers.

While the engine was running (and while it was misfiring) I did NOT see any spark jumping nor did I hear any spark jumping any where. I replaced the spark plugs about 4k miles ago. The wires look good, but I know that can be deceiving. I pulled the wire connecter plugs on each coil and they are not corroded. I also pulled the plug wires off #4 and #7 at the coil and they are good as well.

I DID purchase a Scan tool so if it happens again I won't have to go to the Auto Advantage to find out the codes.

I am thinking that I have a coil getting ready to go???? Anyone have any thoughts on that??? If it is a coil, am I better off buying a FORD coil or are the after market coils okay???? Any one have a suggestion for an online store for parts???