!EGR modify O2's?
you go into closed loop. While it's on it changes the
O2 readings but they aren't being used.
EGR is (supposed to be) chemically neutral gas. The
mixture loop still tries to control to the same point.
Any difference will be small and the trims will take care
of it. EGR is only applied at fairly low throttle, fairly
high MAP so it doesn't have any impact to power
tuning.

