Im confident I found the issue to the P0304 I got out of nowhere yesterday. Recently I replaced one of the valve buckets and while in there I replaced water pump and some timing components along with other things here and there. Car started right up after doing all this work and has been running with no issues.

Yesterday as I was leaving work the car started misfiring and the idle was rough. No SES light until maybe 15 minutes later of driving it finally threw a code. I have an Ultraguage hooked up so I was able to see the exact code P0304. I automatically knew something going on with cylinder #4. First thought was ignition coil as ive already replaced all 6 through out the time ive own the car and these are the exact same symptoms i was experiencing. Anyways got home and inspected. Ignition coil #4 was loose. The small bolt that holds it in place was not tightened so the ignition coil was not seated properly. I must of forgot to torque that bolt down when I did all the work. Anyway so I thought OK this is the cause of the issue. Tightened the bolt down, put everything back together and started the car. Still P0304 and rough idle.
I removed everything again, removed the ignition coil and replaced it with a good used one I had laying around. Everything back on and fired the car up again and no more rough idle and cleared the code. Turned the car off and put my tools away. I turn the car back on to move it and again the rough idle and p0304 comes back on.

At this point im like wtf is going on now??? So I remove everything again. Took the ignition coil off. Now I noticed that the spark plug tube has white corrosion. Like water was in there? I remove the spark plug which I shouldve done from the get go and the spark plug aslo has this white corrosion. I notice the plug from the outside and the ignition coil rubber is a little damp. Tip of the spark plug looks dry and like if the car was running lean. Now im thinking **** maybe the headgasket since theres moisture in the tube and on the spark plug.

I take off the radiator cap and coolant looks fine. No oil/water mixture. So I swap the spark plug out with another one i have. I slap the ignition coil back on and everything else. Turn the car on and the idle is smooth. P0304 gone. Drove the car around the block no issues.
Came to work today (20 miles) and car drove great. No issues.

Do you guys think that because the ignition coil was loose and maybe jumping around that created that moisture in the spark plug tube? Which in turn damaged the ignition coil AND the spark plug? Just curious to see what others think might have happened.

 

I suspect the loose ignition coil boot was causing the spark to jump which resulted in the misfire. Were there any signs of carbon tracking on the plug or ignition coil boot? I suspect the white corrosion you saw in the tube was carbon tracking left behind from the jumping spark.

What I suspect happened is the plug fouled out from unburnt fuel and that may have been the moisture you saw. Damage to the plug can occur under prolonged exposure to raw fuel washing down the plug + cylinder walls. I doubt you have a head gasket issue. Depending on how long you drove the car with this condition, you might want to do an early oil change if a lot of fuel washed down into the crankcase.

For future maintenance and to assist with spark jump issues, I like to coat the inner diameter of the coil boot with some dielectric grease using a q-tip. No need to go crazy with it, you don't want to foul up the sprung contact plate with grease as this can also cause misfire issues. Just a small layer of grease to make removal of the coil easier in the future, this also helps protect against moisture intrusion and spark jump. Need to keep those electron pixies inside!

Cheers!
-Icer

 

Thanks for your input. I just did an oil change a week ago. I didnt drive it too long so i think I should be fine. Bummer I had replaced with the plugs and ignition coil last year. Im not sure how I missed tightening that 10mm bolt on the ignition coil.