I don't know specifically on this engine but on a VAG TDi it's a sure sign that the turbo is overboosting and that the ECU is taking action by reducing engine power to prevent damage. This is usually due to the variable vane ring in the turbo becoming stuck due to the build up of soot and corrosion. I would guess and suspect yours is also a turbo overboost problem. You will need to read the fault codes that are stored and go from there.