Does the actuator rod controlling the variable vanes of the turbo move freely and for the full length of its travel? This can be tested by disconnecting the thin hose which operates the actuator rod and connecting it to a vacuum pump. If it only moves slightly or not at all then the variable vanes in your turbo are more than likely stuck or gummed up. Less likely could be the diaphragm has failed in the control valve operating the actuator rod. If it's the variable vanes then your turbo needs exchanging or overhauling.
