If you have good vac source and normal AIR Pump operation, then the code can be caused by a weak 02 sensor,
The trigger circuit for AIR code is the ECU does a Self-Test and looks at the 02 sensors output to read a VERY LEAN condition.
This common fault is the 02 is no longer capable of such a low {Extreme} reading and the ECU sees this as a Fail and brings on the code.
This takes a lean condition voltage test from the 02 to verify.
A Commonly over-looked diagnosis.........