ALH engine the MAF should go up to around 850. 500 would be a bad sensor. Test the VNT vane control with this article: http://www.myturbodiesel.com/1000q_how_to/a4/VNTadjust.htm you really do have to use a vac pump to test it.
I've had boost hoses blow off and it sounds like it could be a boost leak. The stuttering at a certain rpm, smoke, and the feeling that the boost is dumping all suggest a boost leak. Do more testing. If the intake system won't hold light air pressure than you definitely have a boost leak. If you pressurize it and it immediately leaks off then look for a crack or small leak.
I've had boost hoses blow off and it sounds like it could be a boost leak. The stuttering at a certain rpm, smoke, and the feeling that the boost is dumping all suggest a boost leak. Do more testing. If the intake system won't hold light air pressure than you definitely have a boost leak. If you pressurize it and it immediately leaks off then look for a crack or small leak.