A juddery runner...

I had the same issue a few years back with one I had (1.9Td 2005) it was a dodgy injector. Feels like the power is being cut like flicking a light switch on and off repeatedly.

Injectors for them aren't actually that expensive, especially for a reconditioned one. Get it plugged in and find out which one it is and swap it out.

I wouldn't take it to Darkside, they have a penchant for blowing cars up for a laugh (joke) but I have heard one or two bad stories.