I would be inclined to lean in the direction of a fuel related issue, either a lack of proper fuel enrichment or it is an electronic regulation matter. I believe Bosch referenced that system as the KA Jetronic.

Have you tried installing a new oxygen sensor and resetting the CO mixture? Might be a god start.

Personally, I avoid most rebuilt fuel injection components unless they are made available through Bosch or MB. I believe "spray and pray" rebuliders simply do not value time, be it theirs or mine.