Transit connect 04 tddi engine or ignition advice

[Chrishollbuilder]

Hi all. Iv bought a 2004 transit connect 1.8 tddi and every morning in the last few days iv started the engine as normal but when I rev the accelerator it gets to 2000 revs and dies. Iv worked out that if u turn it off then back on really quickly before engine cuts out it runs fine but a little sluggish. Can any1 help in telling what the problem could be please.