bad idling on my Kawasaki W800

Any help much appreciated, my w800 surges not all the time but sometimes on idle.
It goes from 1300 revs down to almost stalling and then back up again but only occasionally, like when stopped at traffc lights or in traffic.The throttle bodies have been balanced and there are no Fi lights coming on. when I carry out the diagnostic check ie. the short to earth there are no faults.

It starts up fine and the fast idle works fine and the idle is fine some of the time. The rubber manifolds are crack free and someone suggested spraying wd40 on the rubber manifolds to see if it was drawing air, I sprayed it everywhere around the inlet but nothing happened so I assume they must be leak proof.
It had the cup kawasaki exhaust fitted from new but just to be sure I refitted the original peashooters, again no change.
I have removed and cleaned all the connectors including the o2 but no change, as I said it does it every rideout but only sometimes. I cant make it do it or tell when its going to do it. Its done 6800 miles and 1500 have been with this problem, before that it was someone elses.

Any help much appreciated.

Regards
Cliff