Started the car one morning and it vibrated so badly I was scared to drive it. First thing I did was replace the plugs and coil packs. No change.
OK, so I've had the following done:
Replaced all four engine/tranny mounts
Replaced harmonic balancer pulley and serpentine belt.
Replaced timing chain tensioner (while replacing a leaking oil pan, the mechanic found the parts in the pan)
These measures have reduced the vibration about 90% but it's still there, whether in park or driving and, when placing hands on the top of the engine, feels like it's worse at the front (actually passenger side) of the engine. There is no apparent power loss and she's not throwing any codes. Both of my master mechanics are at a loss. Me too. 191 +K miles on it.
Any ideas?
EDIT: I did have a VTECH system failure that cleared on its own after I put half a can of Seafoam in the oil and ran it. Changed the oil and put another half can in before the oil pan replacement. and P1259 code has not returned.

 

They found the timing chain tensioner in the oil pan (Sump)?
That doesn't make any sense. I believe the timing chain tensioner is in a separate volume and cannot naturally fall into the oil pan. What your mechanic probably meant, is the oil pump chain tensioner. Yes there is a separate chain for the oil pump.

Is it possible that your oil pump is producing vibration that shook loose the chain tensioner? If that is the case then it is a matter of time before it happens again. The oil pump can/should be disassembled and inspected for damage/wear on shafts,journals, etc. Also the pump has two balanced shafts that need to align correctly with each other.
When you get down there, try to also inspect the crankshaft (with bearings, piston rod connection, etc).