Codes came up reading PO170(bank1)and PO173(bank2). Need some help.

What is your question?

These codes came up and my car is running really rich. The person that I bought it from said he replaced part of the exhaust because of a leak. I just cleared the codes and my car started stalling after that all the way home. It was idling way to low. It finally stopped stalling and is idling just fine. It usually runs fine with no problems but I wanna fix it. Any suggestions?