Airleaks can be the worst thing to find! I suffered with the same issue as you for months and months... turned out to be the dumpvalve was knackered and staying open just enough to cause the engine to stall.

First thing I would do is check the tightness of all jubilee clips on your main boost/turbo pipes. The other thing is to check whether your dipstick keeps popping out under pressure, that'll create an unwanted air leak too!