That O2 sensor looks very bad. I took out mine on my '91 300E and it was original and just looked heat treated from being in there so long. Spliced in the same O2 you have there and had an instant improvement in idle but had to adjust air mixture to fine tune. I think I may have an EHA issue too but going to replace injectors, seals, fuel filter, and fuel pumps first. Always have hard cold and warm starts for some reason. Idles fine once started.