Nissan - Altima :: Misfiring Cylinder While Driving And Engine Light Came On

I have a 4 cylinder, 2002 Nissan Altima with about 170,000 miles on it. About 2 months ago, the car starting misfiring while driving and the engine light came on. I went to autozone, used their diagnostic tool and it said I needed to replace the fourth cylinder's ignition coil. I ended up just replacing the spark plugs at that point. After replacing the spark plugs, the misfiring seemed to stop, but the check engine light was still on although the car ran great in comparison.

Then, about 2 weeks ago, the car started smelling like gas and slightly misfiring again. I bought set of ignition coils and changed them out. I started it up, the car seemed to work great. I went to the store about an hour later and the car worked better all the way there with no problems. Then, as I was about to leave the store, I started the car up and it started sputtering and misfiring and you could visibly see the engine shaking like crazy when I popped the hood. It stopped shaking, evened itself out, after about a minute. Then, I felt the top each of the coils and the first three were fine, but the fourth had a rapid tapping coming from it that was obviously not right.

I gave it a couple of days, but the car didn't stop smelling like gas or misfiring when starting up, so I pulled out the ignition coils and the spark plugs. The fourth spark plug was brown and burnt from the bottom to the halfway point, unlike the other still-clean spark plugs. My first hopeful thought was, maybe it wasn't tight enough and that was letting gas or oil inside to burn. I tightened it up, put everything back and it seemed to be alright, even the tapping from the coil stopped.

However, within the last couple days, the car has been smelling like gas and feels like it sputters and misfires once I start it up. The misfiring seems to stop after I rev the engine a little bit, but sometimes when I'm idling, you can still smell the gas and sometimes audibly hear a sputtering.

So my question is: what the hell could be wrong? Faulty wires, a stuck valve, bad compression, what? Remember, the fourth cylinder's spark plug was only burnt on the bottom half if that's useful.