The ecu stops using the lambda reading in open loop. Open loop occurs at wot, at a certain map Voltage and when cold until it reaches a set temperature. So you will only notice a difference at the points he mentioned where it's running too lean. Basically your lambda cannot be reading right as the ecu isn't applying enough fuel trim to keep the afrs in check until open loop. Seeing as you have an aem you can just tap the 0-1v emulation line into the lambda wore going into the ecu.. Your wideband will then act as your lambda