M104 rough idle and vibration issues finally put to rest

[Old Geek]

Have been working off & on for last 3 months to resolve rough idle and some vibration/surging at various rpms. After searching through the shop forums, I was able to come up with a list of the most likely 'suspects'; throttle body, OVP, O2 sensor, and motor mounts.

!st round - cleaned throttle body and replaced OVP. Surging at various rpms is gone.
2nd round - O2 sensor replaced, and added Lucas fuel treatment. The W124 now runs a lot smoooother, but the roughness in the idle is now increasing.
3rd round (today) finally replaced the motor mounts. Discovered that the old ones were basically as hard as a wood block. Car now idles smoothly even with A/C on.

FYI -[/COLOR][/B] One minor issue with Motor Mount replacement: I could not find in the forum archives what type & size bolts are used on the motor mounts (my maintenance CD's show a hex head bolt but no size given). On my W124, the mounts were held in with 17 MM hex head bolts for both top & bottom. Also - the Passenger side top bolt is a very tight fit for the hex socket.