I swapped to test your "theory." It proved wrong. My NGK plugs worked perfectly fine in the 300E. And the Bosch H9DCOs gave me the same symptoms. So, the plugs have nothing to do with it.

I like this car, but it is my beater. I don't mind spending money on it, but I'm not going to throw money away for no reason either.

Anyway, back on topic towards a resolution... Will be ordering injectors and a few misc. parts soon. Will see if it helps out the issue.