Cylinder 4 Misfire and Oil on Sparkplug

Hello, recently popped the P0304 Cylinder 4 Misfire code in my 99’ Prerunner V6 3.4L, engine is shuddering in idle and especially at 40 mph+. Stopped driving it of course. Replaced ignition coil and sparkplug, didnt fix the problem. Noticed there was oil within the sparkplug threading and even on the porcelain side which seems unusual. Any ideas what would cause this? Thank you, appreciate the help!

 

Time for a valve cover but more importantly spark plug tube gaskets. Good luck and welcome to TW!

 

Thank you for the info - glad to hear this because this is exactly what my buddy’s mechanic told me last night as well. Ill update if it works, Cheers

 

New valve cover gasket will fix the oil on the porcelain side of the plug, but I can’t see that fixing the error code since it remains after he replaced the coil and plug.

 

Yea I think you have two unrelated problems:
1) Cylinder 4 misfire
2) Spark Plug tube seal

I'd fix the leaky tube seal and see if perhaps that rectifies the misfire, but I'd expect it won't. So your misfire is probably more than likely compression or fuel related (maybe a clogged injector perhaps).

 

Thank you all for the info. it ended up being the spark plug wire that resolved the issue luckily! Next step will definitely be replacing valve cover and spark plug gaskets to prevent that oil leakage.