Although the 1985 380 does have O2 sensing and a feedback circuit, it does not have an EHA (which is part of the third generation of K-Jetronic, aka, KE). 1985 is in the second generation (often referred to as K-Lambda), and is still equipped with a control pressure regulator (aka, WUR). The fine, feedback mixture control is via a frequency valve and its controller.

As the OP works thru the problems, both the WUR and the frequency valve may become candidates for investigation.