Toyota Hilux intermittent white smoke

Hello toyota lucida with intermittent white smoke.had egr valve replaced.had head checked ' had the engine tetro cleaned.car uses no water or oil.had oil changed and all filters ,had transmission fluid changed .had tank checked for water and ok new fuel filter .never runs hot .drives perfect but now and then could smoke for two days then nothing for a month then it could smoke for a day or two.never smokes in a garage or fails its mot.it could smoke i phone a garage to look at it straight away and it stops before i get there.? The smoke is like a cloud cant see behind me in my mirror then disappears .any ideas anyone please .no one can find why !!! Ps not piston drag.white smoke no smell ?