Here's an odd one
 

The Car: 2007 RL with 142,000+ miles. I do nearly ALL the work on the car.
Symptoms: Mildly pulsing idle, and car seems to hang up, or hesitate, prior to shifting to the next gear.
Resolution: Took it to the dealer and diagnosed a failed coil in cylinder #5. Talked to the tech who tells me that there is evidence of "blow by" (his word) and fouling on the #5 spark plug. He then suggests that the rings are failing on that cylinder, and maybe others, causing oil to creep into the combustion chamber resulting in the dark streaks showing on the #5 spark plug.....his evidence of "blow by". The plug was streaked dark emanating from the threads, and the tip was dark, but not concerning. Failed coil replaced along with all six plugs (against my wishes BTW)....car runs like a top!!

OK, as I said I do all the work and replaced those plugs some 35,000 miles ago. I was pretty careful to tighten them after putting a dab on anti-seize on each plug. I asked the tech if is was possible I had not tightened the plugs completely, resulting in the "blow by" marks found only on the #5 plug....he said possibly, and stuck to his guns on the rings potential. Though he did admit that they seemed "a little loose". Car is now running great....just as it did before the coil failure.

Your thoughts?

Any compression number?

The spark plugs are known to get loose over time. I torqued them down to 25 ft lb and a bit past that until I felt it was snugged. I feel if you did any less than that you'll have a chance of the plugs loosening. I experienced this the first time when I torqued them down to 18 ft lb.

Nope. Guess he wasn't THAT convinced, huh?

No point guessing without a compression check.

If you get any low values, a leak-down test is used to determine whether it's rings or valves.

If the foregoing is all Greek to you, find a competent mechanic.

OTOH, if it ain't broke, it probably was just loose plugs - so don't fix it.

Any oil consumption? If you're getting blow by enough to affect engine performance like that, I'd think you'd be seeing oil consumption as well. If not, I might suspect something else.

Be glad it's fixed. Given what he wanted to do, be gladder all he overcharged you for was six plugs.

So I started thinking about the tech's comments about "blow by" and I checked the oil level. Half a quart down after 5000 miles driving since the last change.

My Porsche's spec was half a litre in 2000 km, so with 150K on the clock the half quart seems reasonable.

Change your pcv valve and that might improve. I wouldn’t be worried about that :)