Code P1504
 

First off hello everyone. First post here so hopefully I’m not overlooking the answer to this on here somewhere already. I have a 99 protege with a 1.6l with an auto transmission. CEL stays on and get P1504. Changed the AIC with no change. Car has slight surge at idle and running very rich. I know the possibilities could be an open or shorted AIC circuit, one of the evap solenoids or possibly a plugged cat. Any ideas on where to start checking and how to test these components without throwing parts at this thing.