I hate generic codes. Can you offer a complete discription as to what the code actually said? Was there a problem with the flow and was the signal too high or too low? The only thing I can suggest at this time is for you to check the plumbing first.
Pay close attention to vacuum hoses that connect to items #3, 4, and 5. If the hoses have collapsed or broken, replace them. That will cause air injection problems. Let me kow what you find.