Managing EGR for MPG

[MetroMPG]

Originally Posted by omgwtfbyobbq

But we can't because we can only heat the intake charge so much or we risk pinging, which is why there's no EGR on idle

High EGR also leads to mushy/delayed throttle response, which is another reason it would be avoided at idle - reasons of driveability.

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Another question I've been mulling over: if EGR were "manually" introduced to my engine, how quickly would it respond with correct fuel metering? Initially, would it not lead to an over-rich condition because the engine is pumping fuel based on readings from the MAP and TPS?

Would an O2 sensor respond quickly enough that this would even be a feasible experiment?

Does it even have enough "influence" on fuel metering to preserve stoich A/F mixtures at 20 or 25% EGR?

I don't know enough about O2 sensors.

I suppose the same question could be asked in terms of driving at high altitudes: "At 9,800 feet, for example, there's about 2/3 of the oxygen in the air than at sea level." - source

Even if you were driving at 4500 feet, there may be 15% less o2 available than at sea level. Modern engines must be able to adjust to that, or we'd all be spewing soot driving through some of the passes in the Rockies.