lean miss source
I had 2 MBZ with the CIS. When a 'lean miss' developed at idle, usually caused by hardened seals around the injectors where they fit in the head. Renewing those seals always improved the idle. It also could be dirty injector nozzels, or just plain wear and funky pattern. I always took the set of eight to the nearby Porsche/Bosch shop and had them presure clean and test. Sometimes a single injector will start showing dribble or poor pattern at very low flow.