Bret
From your figures I assume it is smoke emissions for a diesel you are
talking about.
1) use an injector cleaner at each service.
2) before your MOT make sure you change the air filter and thrash the engine
at 4000 + RPM in second gear until accelerating at this speed produces no
smoke from the exhaust ( the cat gets clogged with soot).
Mike

New filters and engine oil before MoT is due. Run the fuel tank down to less
than a quarter full. Put a flask of that injector cleaner jollop (it's
petrol really) into the tank. Twenty minutes before the MoT appointment,
hurry down the nearest ten miles of motorway and then thrash the arse out of
it on the way back. Make sure the coolant temperature is up to normal (or
even a bit more)Straight into the MoT centre and the reading will be so good
you will receive an award for improving the environment.
DaveK.