pistones

iTrader: (5)

dropped in a jspec s5 into s4 luckily it was good.but it has an intermittent smoking problem.it comes and goes when it feels like it. the color is light blue and sometimes grey. it starts strong every time, doesnt overheat and running s4 mop. changed all gaskets without pulling motor apart, and no leaks anywhere. did notice bac doesnt work all the time. also the smoking mostly occurs when the idle sticks at 1200- 1500 and sometimes while driving. it doent smoke when i have it idling at 700-900. this smoking problem is very random, not at every start or at a certain rpm except when it idles high. any clues to random smoking?? im gonna keep diagnosing but if anyone has any input much appreciated.