Motor replaced in 04 honda, rough idle, worse with AC what could it be!.

What is your question?

We had the motor replaced just barely, and it kicked on the check engine light kicked on, and got a code read and it says that it was a exhaust deficiency or something somewhere, how do we tell what it is and what to replace? It does it whenever it's on, it vibrates B's jfmthe time. worse with the ac on, think the code we got for it doesn't