bubbles – the first thing that I would do, if only to satisfy your curiosity, is to contact the EPA and try to ascertain what actions if any they took subsequent to your complaint.
Then, as the offending vehicle shouldn’t be on the Common Property irrespective of its non-compliance with air pollution laws, and as whoever it is that has given a security card to that vehicle’s Owners/s is in breach of your Plan’s Special By-Law in circumstances where neither your Executive Committee (E/C) nor your Building Manager (B/M) is prepared to do anything about that, you should immediately write to your E/C Secretary (cc your Strata Manager) advising that unless you receive a written response to your past complaints within say 7 days, then as an initial step you’ll be lodging an Application for Mediation of those complaints against the Owners Corporation with the NSW Office of Fair Trading.
Your Application shouldn’t be about the exhaust smoke, but be about your Owners Corporation (incl. the E/C as its representative) not acting to rectify breaches of your Plan’s Special By-Law regarding security keys, and the Model By-Laws 1 & 2 relating to noise (the exhaust) and to vehicles parked on Common Property.
Just ensure that you have properly documented everything, including the details of your initial complaints to the E/C and to the B/M and about the visitors to your Unit.
As a matter of interest, did you follow-up with Council regarding possible breaches of the Conditions of your Plan’s Development Consent?