1995 E320 w/207K miles ( 104.992 engine )
I recently did head gasket and valve cover gasket replacement, including all the rubber washers and seals that are associated/accessible during those jobs. Also wiring harness replacement.
Drove the car for about 500 miles and almost all seems good. The car runs fine under acceleration but when coming to a stop there is a slight miss at idle. When I press on the accelerator the engine will dip to 500 for a second before RPMs climb and it smoothes out. If I come to an abrupt stop the idle will fluctuate between 500 to 700 for about 10 seconds before it levels out to 550 with a slight miss.
I decided to replace the spark plugs and the connectors hoping that would be the fix. Previous plug change was at 180K using Bosch platinums. I was really surprised when I pulled the spark plug connector from cyl #1, the connector came up drenched in oil. The spark plug was sitting in a puddle of oil. The bottom of the plug that faces the cylinder seemed dry, though tough to tell because as I pulled it out the oil that was sitting there would have run down the plug. However, there was no smoke when previously running the engine so I assume there is no oil problem in the cylinder itself. The other 5 plugs were dry. On a side note, I am surprised that all the spark plugs were about 90% worn, there was almost nothing left of the tips. Aren't these platinums supposed to be good for 100K?
Anyway, back to the subject....I installed standard OEM bosch plugs and new connectors. When I started the engine there was quite a bit of smoke, I guess that was from the oil that leaked down into the cylinder when I removed the spark plug. After a minute or so the smoke stopped (burned off?) and the car runs just about the same as it did before the plug change.
My bigest concern is the oil in the spark plug housing, can anyone help with ideas? Could it be a dislodged rubber seal or washer from the valve cover kit?
My second concern is the slight miss, would the first step be to search for vacuum hose leaks?
My third concern is what caused the old plug to wear so fast.
Hope you guys can help with ideas.