[W126 Coupe] idles rough when properly lean

[Dick Spellman]

Hello Richard:

Fast not too technical DIY stuff would be inspect the cap and rotor with 30k
miles the rotor should be worn a bit inspect cap for traces or cracks.
With a rag pull each spark plug ignition wire and listen for a further
stumble, if you find one cylinder where there is no change this is the
problem your mechanic needs to look at.
Spray can of carb cleaner with air filter housing removed is a fast way to
check for vac leaks, work the spray around the air guide housing and up
under the fuel distributor then along the new injector seals and hoses
looking for the idle to smooth out.

Dick