hi all, have a small problem with me truck,when reving in neutral at about 2000 rpm you get a small misfire and puff of blue smoke, and if you keep revs up at 2000 and rev from there it does the same, on tick over no misfire dont even notice a misfire when driving, but do notice at night in headlights behind when accelerating crap out the exhaust,done a code flash test came up with code 55 no fault found, got new k&n filter cleaned maf sensor but still no different, drives no different no lack of power so im at a bit of a loss, so as the title says wot do you think ? thanks in advance eboy. sorry its a bit long winded: