hesition problem below 2000RPM

I have a problem with I think either the fuel or ignition system. MK1 GTI 1.8 1985.
The car seems to idle fine though when you pull away there is a hesition, it is almost like and sounds like its running on three cyclinders. As soon as you hit 2000+ RPM its settles and runs as normal.
No idea what is cuasing it hence this post, all help apprechated….

Sounds like incorrect ignition timing.