I can easily understand your frustration and my suggestion to install a pair of Webber carburators to replace the Bosch system was simply to tell you the options exists. In my mind, it's not the way to go.
You are trying to fix this problem with the hit/miss/hit/miss approach which is not the most enjoying and economical. I personnaly have some knowledge/pratice and habilities but I know when to turn to a pro when it surpasses my degree of competence. A year ago, I had a hard cold start/rough cold running I tried to solve by throwing parts at it. I leaned my lesson.
I went to my thrusted/expensive/hard to catch/independent pro who, for $37.00 diagnosed and repaired a loose electrical connection.
I admire your persistance in trying to solve your problem Good luck
JackD