loose spark plug wire boot
I had been getting some smoke and slight vibration, so I checked my wires. (They were replaced with OEM about 5 months ago).
Lo and behold, the 3rd wire from front on driver's side (420 SEL) was loose at boot. Upon removal, I found that in addition to being loose, white powder gunk had clogged the boot and the inner recepticle preventing it from properly inserting all the way.
After I cleaned it out and plugged it all the way in, car seems to run stronger with less vibration.
Also, smoke appears to have disappeared.
Does all this seem logical?