A little Mercedes vacation trip tale

[donbryce]

On our way to Bar Harbor ME, gorgeous sunny day stuck in traffic waiting over an hour to cross border (4th July next day), trusty 380SE idling smooth as glass, A/C working great, cruise control amp resoldered (again) and working A-1, what can be better? Arrive 2 hours later in Ellsworth....Oh Oh, engine missing at idle, blue smoke....stop for buying, get back in traffic, missing and stumbling, oil smoke big time.....get to motel, car is literally shaking at idle! The missus doesn't look worried though, after all, we have an on-board mechanic right (me)?
So I'm up real late trying to sleep and diagnosing at the same time...concluded it could be vacuum leak (happened before, just a hose off), or one cylinder not firing right (oil getting in there somehow). AM, pull off air cleaner (motel lot fixes no fun on vacation), all hoses seem OK, so figure must be fouled plug.
Got home OK, with lots of rough acceleration, but running fine at highway speed. I pulled every plug, all looking good, then got to #8....what a mess! Looks like something went wrong with this cylinder during my valve stem seal replacement 2 years ago. I doubt it's the oil ring...but I did overfill the pan a month ago, since corrected, so perhaps the oil pressure 'unseated' the seal(s), or maybe the guide(s) was worn and the seal didn't stay on...or..well, I'll post an update after further investigation.
The moral is...trust yourself with your diagnostic abilities, don't worry over seemingly 'major' stuff when on holiday (Mercedes engines are tough enough), and limit the discussion of mechanics with the missus to keep her calm....