If it's the AEM causing the CEL, there are only two ways of solving it:
1. Do this mod:
new[b]celica
[/b].org/forums/showthread.php?s=&threadid=127861100% success rate on all cars that have tried it, and all test cars have had CELs and/or bogging before it.
2. Buy a TPR CAI. It has the above mod integrated into it.
The CEL will keep coming back no matter how many times you reset the battery, and any other intake will cause at least bogging, and most likely CELs as well.
As for headers, the current crop of headers are crap. They barely gain any power at all, and sometimes even lose power.
https://celicahobby.com/ubbthreads/thread.f0_1870260135_0_collapsed_5_365_1.html#1870260135Wait for TPR's true 4-2-1 header. Totally different design which is optimized for higher flow than the other headers (which all use the stock design
).