my car had similar intermittent rough idling / stumbling immediately after the hg job. the only clue was that after touching one of the leads to the injectors it smoothed out. i should perform an autopsy on my harness as it looks perfectly fine except where my local indy tried to see what was wrong with the leads - there you can see large sections of wire are bare. that section that steve opened up in the picture goes underneath the intake manifold and has the leads to the injectors...
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"