Power loss issue/ Check Engine

[gammanuc]

I'm having a power loss issue and a CEL. I can be just cruising at a constant speed when all of a sudden it feels as though I just dropped some horsepower and the check engine light comes on. I have to press the accelerator further to keep the same speed and of course gas mileage goes way down and when I decelerate I get some massive backfires. If I turn the car off and on again the issue goes away for a few minutes.
The CEL is:

Learning fault in lambda (air fuel mixture adj)

Possible causes: vacuum leak, oxygen sensor, air mass meter

I have a new oxygen sensor, I replaced the AMM (with a used unit) and the
vacuum is at -16 psi at idle -22 psi on deceleration and boost is fine.

I do have a small leak at the fuel pump flange seal could that cause the problem?