Ford Escape / Hybrid :: 2004 - Intermittent Rough / Low Idle / Misfire On Startup

My g/f's 2004 Ford Escape (3.0L V6 AWD 112,000mi) is acting up. After a full day of sitting, with the second half of it raining steadily, she was driving her Escape and it was acting funny (miss-firing, she said). The engine light came on and soon began blinking. She got to my house shortly after it started this. We left it and I drove for the day. Later that night, I drove it and it seemed fine. The engine light was on, but not flashing anymore.

The next day I took it my friend that was a Saturn mechanic and now working at a KIA dealership (same owner as the former Saturn and current Buick/GMC and Chevy Dealer). It ran fine for me. So he tries to scan it, his Mac Tools scanner won't read it. The KIA scanner wouldn't read it. I drove it the Ford dealer up the road. They said they couldn't get to it until after lunch, I just want the codes read. They re-iterated, and I told them to pound salt and went to an independent shop where I know a guy. They read it right away for me. "Mis-fire on start-up" & "Cylinder 4 Mis-fire." were the two codes stored. He cleared them.

She got the tune up basics (plugs, wires, air filter, etc) and did the complete tune-up herself yesterday. (I was impressed). She put 94 in the tank and some fuel system cleaner in it as well. She said there's been no change and today I finally saw what it was doing. Sometimes during idling at a stop light, the RPMs will drop to almost zero, the lights dim but so far it has not stalled. It'll do this for several seconds, then correct itself and idle normally.

Currently, the engine light has not come back on. She's thinking coil pack (each cylinder has a coil on these engines) on #4. She wants to switch it out with #1 and see if the problem follows. I think that might uncover the cause, or it could be the battery. It's the original, never been replaced and has a lot of miles on it, but it survived this past winter, without trouble. In my experience, most batteries crap out due to age in the fall when the cold snaps start.