my xr3i rs turbo won't start from cold any idears?

I've got a mk4 xr3i cab with rs turbo in its won't start from cold I have to bump it then wen worm will start off the key but have to keep the revs up or will just die out then wen cold won't start agen but but also every time I turn the key it fires to start but don't then turn off then turn to try agen fires to start then don't same every time unless worm runs fine just have to keep the revs up a lil bit any idears plz