I replaced my stock spark plugs a few weeks ago and noticed that there was oil around the threads on one of the plugs (furthest right one, i.e. passenger side). The rest were fine. What could this mean?

Also, the engine doesn't idle very smoothly. You can sometimes feel a "knocking" feeling, although I doubt that it's actually knocking. I changed the spark plugs for this reason, and it ran super-smooth for a few weeks, but the problem is now back.

A bit concerned - it's a 2006 GT with less than 60000km on it!

Other notes:
-I switched over to synthetic oil since the last 2 oil changes.
-It has a FRAM oil filter right now, not sure how it compares with OEM.
-The new plugs are E3 Diamondfire.

Ideas? This is my first post on this forum so be nice

 

A couple changes ago, I spilled oil when re-filling and the plug you mentioned is the closest to the oil refill. Though on my 2007 GT there is a lip to keep such things from happening. But if there was enough fluid it would overflow, or if someone had the plug coil removed during oil filling. I guess the factory / dealer could have done this by accident as well.

Have you noticed any benefits (mileage?) with the synthetic oil?

I've got a somewhat rough idle, just seems like it's an almost miss. During warmup there's a missing / surging as well as the engine computer runs between fuel maps when under load.

 

That's a good point. I had accidentally left the oil filler cap loose for a few days when I first bought the car and got oil splashed all around the area, so it's likely that oil could have seeped past the ignition coil boot. Puts my mind more at ease, thanks.

As for the synthetic oil, I couldn't give you an accurate answer since I switched over one oil change after I bought the car. Combined city/hwy driving is about 8-9L/100km, city driving is about 9L/100km (calculated, not the inaccurate reading from the ECU). I mostly use Castrol Syntec 5W30.

 

ooh, conversion time - that 8-9L/100km is 26.1-29.4MPG for the US folks... which is about what I get using mobil 5000 5W20. I got 35mpg (6.72L/100km) on the highway, and right around 30 (7.8L/100km) in mixed driving depending on the temperature. When it's cold (like 5F / -15C) & the car is running when scraping snow off etc... i'll get down to 26-28 (9L/100km).

 

That sounds about right. It's getting quite cold here in Canada, hopefully I get through the first winter with my 3 without any hiccups!