What the heck are you burning?? Only kidding! The theory is that when oily crankcase fumes leave the valve cover through the hose near the oil fill hole they are directed into the air intake. The EGR valve near the turbo at times vents hot exhaust into the air intake as part of an emissions control scheme. Hot gas plus oil laden air combine and cook depositing carbon on the inside of the air intake areas. On my 603 motor the carbonation starts in the crossover pipe and into the intake manifold itself, You can disassemble these parts and witness this phenomena. you can also pull any of the various plugs and outlet adapters attached to the intake manifold and most likely the portion exposed to the inside of the manifold will be covered/encrusted with thick black granular carbon. If this type of carbon deposit restricts or blocks a manifold pressure port your boost system doesn't know what the manifold pressure is and in the case of turbo boost can't signal the ALDA to increase fuel proportionate to the turbo's boost. The problem is the turbo boosts the air charge but without a corresponding fuel injector boost there is no more power generated. Essentially the engine has a turbo air supply and a conventionally aspirated fuel supply = no extra power from the turbo setup. If you don't feel that extra power kick in significantly when your RPMs get in the 2500+ range you may be experiencing this problem. Conversely if all of a sudden you fail to experience the power surge your boost signal port/line might have just gotten blocked!