jumpy revs during idle and running 1.8 b4 wagon

[BARGE-PILOT]

as title suggests,when it starts up sometimes the revs jump straight to 11-13 then dive to 5,then they duck and dive,it also does this while under power.if I blip the throttle it occasionally settles to around 10 until the choke lets off but not always,it appears to be getting worse or at least more common,the car never stalls no matter how low the revs dip and it dosen't follow a pattern as such, its very erratic.

it has me stumped,otherwise it mostly runs fine.
any help/suggestions will be well received.
Bryan