Fluctuating idle speed HiJet efi 2002

Hello everyone
my van drives fine but has started fluctuating at idle. From cold seems to run a little faster than normal but then drops and revs up again constantly. It is perfectly smooth when driving with no throttle ie. doesn’t surge but feel it must be a sensor issue. Can anyone give any pointers?
Thanks
Flora

1.0 or 1.3? Have you checked the coolant level?

Sorry missed your response there. It’s a 1.3. The problem turned out to be lack of coolant circulation through the butterfly bypass valve on the bottom of the throttle body. This was caused by a blocked pipe union at the cylinder head due to corrosion.
The bypass valve can be tested by removing the intake pipe and blocking the large hole in the bottom with a finger-the engine should now run normally if the valve is faulty .It is likely the coolant is the issue with this valve.

Thanks for the update, glad you got it sorted.