He would (definitely) have come (if the conditions had been right).
He could have come. ~ He would have been able to come. / He was able to come. / Maybe he came.
(It depends on context.)
I would (definitely) go (if the conditions were right). / ~ I used to go.
(It depends on context.)
I could go. ~ It's possible that I will go. / I may go. / I
might go. / I would be able to go. / I was able to go.
(It depends on context.)
These expressions have many related but different meanings, so it's not
really possible to provide a single definite answer to your question.
CJ