JTD juddering

Hi,
I noticed a few weeks back the engine almost cut out and the injector light came on. After revving it seem to clear and drove home normally but the light was still on. I stopped the car and restarted it, the light now went off. That was three weeks ago, yesterday I was travelling along and the same thing happened but it will not clear, I have tried the most obvious changing the fuel filter but still the same, any ideas guys or girls ?