Ok I have a 99 Z M6, SLP lid, and muffler recently had a cat rattle lose the internals and found someone to cut them off cheaper and quicker than a replacement, before they were cut off I noticed a slight flat spot during acceleration no matter what gear or rpm and a P0430 once in a while that would clear and go away for about a month. After them being cut off the flat spot has gotten worse and I'm getting two P0430 and two P0420 codes that won't clear for more than 10 min. Could it be the fact that the codes are thrown and its telling it to run rich, or could it be the O2's sensing a knock (if they do in the f cars) any advice or help is welcome. Thanks.

 

No, they don't care about fueling. I would buy a OBDII scanner (can be had cheap on fleabay) and see if it's KR. Could be running lean too.

 

That's where I got the code numbers, I'm using a pocket scanner. What is KR?