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+ another one for different cars, different DFCO criteria.
Some vehicles may not use it very much, if at all. With DFCO there is air, admittedly a small amount of it, being blasted through the catalytic converter. That tends to cool it so there may be conditions where the capability of the cat. to reduce emissions is being protected (DFCO inactive), despite the readily apparent criteria being met.
In addition to the TPS and rpm inputs there's usually a MAF or MAP criterion. High airflow or manifold pressure will kick the ECU out of DFCO.
ECU's will do some interesting things while coasting. I can observe a constant MAP signal while coasting, regardless of differences in speed or gear. I suspect the ECU is moving the idle air control to prevent the MAP from dropping while being motored, avoiding unnecessary pumping loss. (Called sail on.)
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