Ok so I got a CEL and had Autozone scan it and it pulls up P0420 and P1129....the first one online i read is that the cat is no good or its a common test pipe code but i dont have a test pipe. So the what should I do switch out the cat for a used one or would putting the 02 spacers be fine and not do any harm? I have had a backfire here and there but only when my car was running weird and somehow was running pretty rich (guessing due to my 01 ecu running my f22) since i can smell it but i did the ECU relearn, cleaned the IAC vavle, the throttle body /plate and now the car runs like normal. Which brings me to my next P1129 CEL which when I looked around online the symptoms are usually eratic engine behaviors like rough idles, high idles, bogging and others i forgot but as I stated before ive done the ecu relearn recently and other stuff so could that have caused the P1129?