A4 quattro ('99) idleing erractically

Hi All,
I could really use some help with my '99 quattro- When idleing normally it sits on 900-1000rpm. But for the last two days, it's been intermittently fluctuating between 400- 1800 rpm and has started stalling/cutting out completly in the last few hours. I've just changed the spark plugs, and the fuel filter (currently still covered in fuel!). I don't think its the fuel itself as i haven't filled up for a week. (oil's full.)

I was thinking injectors? (But only guessing as i'm at the limitations of my knowledge!)

Hope for some much required assistance.

Sounds like secondary air mate, have a general squizz at your vac pipes etc, then failing that get a laptop plugged into it to check for faults and have the live data checked. If it was fine before you serviced it go back over all the points you done
Cheers
Jmac