Alright so I got a call from my folks saying that my mom's 02 Taurus SES DOHC was having some issues. My mom had been using it for running some errands and after leaving the third store it started shuttering. They didn't know what it was, but my dad took it into an O'Reilly's and pulled the codes. Turned out it only had one code, which was P0316, which corresponds to misfire on startup.
So I went down to their house this afternoon and took a look at it. I pulled the codes again with my scanner and found that it was also showing P0301, which is misfire cylinder #1. So I had the following thoughts going into this...
1. Spark plug well full of oil
2. Spark plug fried
3. Plug wire fried
4. Coil pack fubar'd
5. Bad injector
6. Bad injector wiring
Alright so I pulled the UIM off and upon doing so found that there were splits in the rubber hoses for both the valve cover breather lines as well as the line for the EVAP system coming out of the UIM. I looked over all of the wires and plug wells and found no oil (scratch #1). I took all the plugs out and found nothing wrong with them (scratch #2). Took cylinder #1's plug wire and stuck a test spark plug in it and had one of my brothers ground the electrode and turned the car over, definitely got spark (scratch #3 and #4). Hooked all of the plug wires up and started up the engine (with the UIM off still). Looking down the LIM we compared the fuel injector patterns, all appeared to be operating the same and normally (scratch #5 and #6). So I put some dieletric grease on all the plug wire connections and placed new gaskets on the UIM and reassembled everything and in the process replaced the split hoses/elbows on the breather and EVAP lines. I then cleared all the codes and disconnected the battery. After taking a break for dinner I hooked the battery back up and started the car. Everything ran as it did before, unfortunately I could still feel and hear something wasn't running right. I drove the car around and it felt a little under powered, with the occasional hiccup ever now and then while driving around. The engine light however remained off through multiple start ups and test drives. I've heard of vacuum leaks causing misfires in some instances, but now with everything fixed I'm out of ideas. I'm thinking of buying a new set of wires and possibly a coil pack, but I don't want to just through parts at the car especially when I could find nothing wrong with those components. I went through the car about 3yrs ago when the rear back had an oil leak in the #5 plug well. At which point I replaced both valve cover and well gaskets, spark plugs, plug wires, fuel filter, air filter, UIM gaskets, ATX filter & pan gasket, and did an oil change. Since then the car has had roughly an additional 60k put on it (putting 99,938 on the odometer).
So I am out of ideas and would be interested to see what all of you think I should look into next.