You could block the EGR pipe. This was faulty on my old bus and it produced great puffs of black smoke (wasnt closing properly = unburnt fuel pushed through exhaust) every time I accelerated.
A blanking plate stopped the gases recirculating when they shouldn't and no more smoke, emissions at almost 0 and better mpg.
thank you, i did not think a petrol engine had one, i will look later on my daughter is driving it at the moment.