Rough running below 2000rpm

Hi all,
Ive got a 1989 Mk1 1.8gti Cabrio with an 8v K-jet engine. I've had it for about 7 years and has been running great with a few of the usual issues (filler neck replaced 4 years ago etc). I used to use it daily for work but in the past 6 months i only use it once a week or so, and its been off the road for the past month having the clutch replaced.
It was a real pain to start after the month of no use and it ran really rough when cold with the idle going so low it was almost at a stall, although this seemed to improve when it warmed with the idle consistent. I took it for a quick drive aroound the block and between 1000-1500 rpm it miss fires and runs really badly, get it over 2000 and its runs perfect. Repeated it today, started easily but again really rough below 2000rpm, i took it for a longer drive along a dual carriage way and it was fine, until the revs drop and the problem returns.
If its at idle (or below say 1500rpm) and i accelerate slowly it seems to be ok, but if i floor it, it missfires until the rev creep up and then it picks up.

Any ideas?

Cheers

Chris

I'd have a look at the electrical side of things first, try plugs, leads, rotary arm, dizzy cap. If all that looks good then try fueling.

I had a leaking injector on my golf before I took the 8v engine out, where it would run lumpy for a while until it was up to temp.

Try the easy stuff first tho If I were you!