Focus 1.6Se 2002 Petrol. Idle Hunting When Engine Warmed Up.

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My Focus has a habit of its rpm's dropping to about 5 or 600 revs and raising up to about 900 to 1000 rhymically when your stationary (hunting), only when its reaching normal temperature,but dosen't stall. Its strange because when you push the clutch pedal down the rpm's settle to normal (not hunting) Any ideas?. it has new pcv valve and hose,i can't find any air leaks in the induction system ,new icv,Vss,Tps,Ford plugs and Ford leads. Do you think it might need Pcm update if so how much is the update.