Corsa emits blue smoke ?

Our Corsa SXi cdti 2005 reg diesel emits blue smoke a short while after starting up then stops smoking again after a while. Car runs good,no problems there, no lights show on dashboard, doesn't waste oil or diesel but the blue smoke sometimes is excessive and is very embarrassing when at traffic lights and other motorists keep looking. Nothing shows on diagnostics. Garage says it's the air mass meter that needs changing, which when unplugged does stop the smoking, but we want to be sure this is the problem before we pay out any more money and maybe still doesn't fix it. We already had the Egr valve replaced when told that was the problem but to no avail! We don't want to leave it unplugged as the light comes on on the dashboard then!