97 non turbo fault codes.

My 97 Eclipse started giving a fault code yesterday ( check engine light).
code 12, 31 and 55. The car still seems to run fine. What is causing it? the IAC valve or Airflow sensor? I tried disconnecting the battery to reset the codes but it comes back.

Thanks!

Gene

The only one is 31. It is the EVAP system :p
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