What part is it exactly that isn't legal? Warming up a car, or leaving it running unattended? One of those I can see being easily defeated in court ie; the defroster on most vehicles is provided with warm air from the heater core, and as such, needs the engine to run for long enough to build sufficient heat in order to clear the windshield to allow for the safe operation of the vehicle. The other aspect, leaving the vehicle unattended, not so much. I'm thinking the basics here are going to be you need to be inside the vehicle, at the controls during the warm up period. If that's the case, I agree.

MV