New plugs and new coils and still misfiring.

[O_HERNANDEZ01]

Hi guys, I have put over 100,000 miles on my non-turbo S60 with no issues until this week. My car was misfiring pretty badly a couple of days ago and threw the PO302 code for cylinder #2. Since the spark plugs have about 10,000 miles on them, I decided to go ahead and put 5 new coils in (the car has almost 200k with the original coils). After I finished changing them I took it for a drive and the misfire was completely gone (ran it for 30min). It also ran normally the next day on my way to work. When I got off work it began to misfire just like before so I drove to the auto parts store and bought a new spark plug for cylinder #2. After changing the plug the problem again went away completely until the next day. It now misfires ever so slightly on idle (like once every 20 seconds) and it does not misfire during acceleration until I hit about 60mph or go up a steep hill. I think it is worth mentioning that when I changed the spark plugs 10k ago I did not put in OEMs. I've heard these cars are finicky with non-OEM plugs but didn't think much about it until it started acting up. Also, when I changed the plug in cyl #2 I noticed the well has a slight ring of what looked like oil around the inner part of the well (kind of where two pieces of metal meet). It looks almost like it has a slight oil leak although there was no physical oil on the plug. The well also generally looked kind of dirty when compared to the other plug wells. Not sure if this is relevant but thought I would mention it. Anyway, I'm not sure where to go from here so I would greatly appreciate anyone's help! Thanks in advance!!

[JeffHicks]

I've been told that anything but Bosch or OEM Volvo spark plugs are subject to problems, so that could be your issue.

That slight oil leak very likely came from the o-ring that fits between the head and cam cover. If there's no oil on the plug itself I wouldn't worry about it, because the fix is pretty expensive.

[harryhendo]

Do you get a check engine light when the engine stumbles?

You don't state the year of your S60, but it should have a OBD-II connector. You can use a code reader to identify the cylinder upon which the misfire is occurring. Swap the plugs around to see if the misfire moves to another cylinder, then replace the failed plug.

Personally, I always buy the official Volvo plugs at the dealer, $42 for a set of 5, as I believe they work best, but that is just my humble opinion.

[chrism]

"...Swap the plugs around to see if the misfire moves to another cylinder..."

In addition, while you're in there, move the coil from the problem cylinder to a different cylinder, but not to the same cylinder that you moved the suspect spark plug to.

What kind of spark plugs are you currently using?