86 Starion smoke problem?

my 86 mitsubishi Starion 2.6L stock Turbo/intercooled, everytime i hit any boost, when letting off the throttle, the car will start to smoke amazingly bad. i also have about 3 cracks in my exhaust manifold. i was told that could be the reasoning for burning oil when i let off the throttle. i replaced the turbo numerous of times and checked my PCV valve, checks good. the car has 160K miles yet the car runs great. beside the fact some time it wants to die at idle. could this just be because of the exhaust manifold?