Lack of power

[Passat_ben]

Have an intermittent fault where I lose power with a long turbo lag in each gear, sometimes all power is there and the car pulls like a train being the 170tdi sport. Problem first occurred when glow plug light came on and take to garage message. Car went into limp mode and have no power. Fuel was low so when fuelled up light had gone but still lacked power however not in limp mode anymore.

Any thought?