2000 LX Focus High Revs!

[Brightspark]

Hi All,
I have just recently acquired this vehicle, in the mornings or cold start, revs roughly are 1000rpm no problem here, put in gear to move off put clutch in to change gear and revs go to about 1500 - 2000rpm, when vehicle has reach normal operating temp/when autochoke goes off 700+/-rpm, vehicle drives lovely. Have replaced HT leads Air filter and oil and filter but no change. Any info would be very much appreciated.