The point of my previous comment is that the accuser (cop) MUST prove his case beyond a reasonable doubt in order to make his charges stick.
So long as drivers do not admit they were idling there is no way a cop can prove it.
What's he gonna do, hook up a certified (by the state) tachometer to the offending engine to support his claim the engine was idling?
Which is what he would have to do to prevail in court (so long as dummy driver doesn't admit he was idling).
Stupid laws passed by stupid politicians for stupid people.