hey guys, seeing if anyone has had this problem or may know what is wrong... took the proto in last week to have the exhaust mani replaced. mine had several big cracks in it and i dont have the tools to do it myself :/ , so i bought a used one with 82000 from a member on here. when i got my car back it seemed to be running well. afr's were a little off and first but not to far. later that day and over the past few days it has gotten worse. i have had my engine light come on twice. it idles rough sometimes, it is running very rich (12 afr when cruseing, sometimes down into the 11's), and my gas mileage has gone down dramatically. when i took it back to the shop that had worked on it, the scan they ran came back with "lean bank 1" or "bank 1 lean", not entirely sure? could the new mani messed with the current tune this much? has a plug gone bad? any help is appreciated