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You don't need to make full time WAI, you could make similar flap like old carburettor cars had, exhaust heated air came from pipe and fresh air from another, mechanical temperature sensing element adjusted flap so that there was constantly around +20C air going into intake manifold at cold weather.
One could do that so that he gets full heated air during warmup phase and then flap would change to fresh air?
I remember reading from some study that it was around X% (maybe 4%) increase in fuel consumption because of EGR, but I can't remember if that was diesel or petrol. In that study there were three methods compared, one being EGR, at least one other was injection of something which I can't recall by name, those other methods did not increase fuel consumption and were better at controlling emissions too. However because of my poor memory I can't now locate that document, can't even remember if I linked it here some thread.
It might be saved to my other computer as it can't show PDF documents unless I save them first, if I find it, I post it here, that might provide some interesting points again.
From my experience, when driving longer distances, if I disconnect EGR wires, it improves economy small amount, certainly under 5%, in my mechanical turbo diesel, which has catalyst installed. That I have tested with thousands of kilometers on and off, so I'm sure that it has effect. Another test would be to clean it up as it probably has not been cleaned for 300 000km, that might change things a bit, I guess.
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