Engine almost dies and slips to limp mode.

[Dubman]

Hi Guys

Need some advice. I was sat idling at some traffic lights, when the light turned green there was no power as if in Limp mode. No lights on the dash. I switched off and re started the engine, all seem to work fine.
I had a code for the fuel rail valve which i swapped out a couple of weeks ago. can anyone add any advice as to what to check?

Thanks in advance.

Simon