Here is a good test that will help pinpoint the root cause.
Under safe road conditions, a wide open throttle acceleration is performed. Try to maintain WOT for at least 5 seconds. 10 to 20 seconds would be better. (this of course is when the problem occurs)
What will the pre cat oxygen sensors do?
Will indicate rich
Should the barometric pid change?
Should remain stable! Very important!
What will air flow do?
Max out. Volumetric efficiency. Engine load 100%
(Engine load Parameter on scan tool should go close to 100%)
Poor acceleration, rich exhaust, and good Barometric pressure = restricted exhaust or late ignition timing.
Poor acceleration, rich exhaust, low or decreasing Barometric pressure = intake path restricted
Poor acceleration lean exhaust and good barometric pressure = fuel delivery concern.
Poor acceleration, lean exhaust and low barometric pressure = air flow measurement error. (Ford has this problem with Mass air flow sensors)
Note: Some vehicles Barometric pressure is not updated until Wide open throttle.