[cnavarro]

There is no 'fooling' the ecu. The difference in temperature is still within target of what is considered an engine that is completely up to temperature. There is a threshold for warm up enrichment that if the engine is not to temp it will throw a code. Also if short or long term fuel trims are outside their allowed range of correction, that too will throw a Porsche specific code.

I don't have Porsche specific figures (I'm sure there is some person somewhere who knows this), but it would appear that cold start enrichment on a modern engine usually stops by 160F. The engines continue to operate at their target AFR, be that stoichiometric or not. OBD2 code P0128 is thrown if coolant does not reach 167F after a prescribed warm-up period. Even in sub-zero ambient air temps, with the low temperature thermostat, coolant stabilizes at 172F.