Just reading my 'Glenn's Mercedes Benz repair and tune up guide...

[Larry & Norma]

Referring to the section on fuel injection. The IP is so finely set up that the
fuel delivered depends on pressure and diameter of the fuel lines. This is why
the unions have to be carefully torqued to avoid distortion of the lines also
Mercedes suggest 'replacement of all lines at 45000 miles' or have the lines cleaned with
very high pressure.
Could this be why my car was running richer after I had the lines zinc plated?
Took 3 clicks on the IP to get the CO reading back down.

[ja17]

It is not unusual to have to make adjustments on a newly re-conditioned injection pump. Each engine is different and each engine is tuned a bit different. Replacing injection  lines seems to be a bit of over-kill although I have seen lines coming back from the platers, with debris inside.

[wwheeler]

When I got my injection lines back from the plater, I blew carb cleaner in a spray can through them to make sure the were open and to flush the debris if any.

[Larry & Norma]

The point I am making is that my car ran richer after plating implying more fuel getting through.
Could this be that the cleaning process used before plating had removed years of 'gunk' build up
within the lines thereby increasing the internal diameter of the lines.?
We see a lot of IP issues on this site, could having your lines cleaned be something that is overlooked
and fairly simple to do

[ja17]

The other possibility, is that debris left in the injection lines after plating,  moved to the injectors, keeping them slightly stuck open,  causing a rich running situation.