Did the smoke appear after the timing tweak? If so, smoke can be indicative of less-than-optimal timing advance. Since the injection timing advance increases with RPM, advancing the idle timing may push the high RPM advance too high and result in some mildly incomplete combustion (from early injection).

If I ever set the ignition timing on gasoline or diesel engines, I always set it to the maximum factory tolerance. For example, the timing advance spec on my Peugeot TD is 7.0 deg BTDC +/- 0.75 deg. I set it to 7.75 degrees BTDC. This gives a little sharper throttle response (as you noted), but keeps the engine's smoke output pretty consistent.

The same thing has been done to the 190D when I replaced the seals on the injection pump. Now it feels a little closer to its 93bhp spec.

-Joe