They can't tell you to go and get emissions tested because of a blackened exhaust...ALL cars have black on the inside of the exhaust???
As far as I know the only department even able to comment on emmisions in QLD are the Transport Department...and they will test on the spot at 4,000 rpm...with no load though you should be running fairly lean.
If they were really interested in emmisions they'd pull over every other car in the Logan district.
Ring a Department of Transport testing centre, they'll probably dismiss it, as it wan't an authorised officer that issued the ticket, and the fact they didn't see smoke and just inferred that it *probably* is running rich.
The general police can't comment on anything that is beyond their professional knowledge, that includes emmsions and quite a few other things...that's why the Transport Department exist, they know the rules backwards, but you don't see them arresting people...it's not *their* job