engine racing on

Help I've got a 1800 Zetec Ford Focus Millennium Edition car.
Problem
When I drive the car at 60 mph the car runs fine - if I dip the clutch the revs on the car drop to 800rpms like they should do.
But if drive the car at 60 mph and take the car out of gear the engine races onto about 4000rpms until I put the car back in gear.
The problem only occurs when the car is warm.
If I approach a junction, I come down the gears 'if there's time' but come the last couple of yards I take the car out of gear and coast to a stop - this is when the car again races onto 4000rpms and when it gets there it returns to 800rpm or if the car stops it returns to 800rpms.
I was wondering if anyone has had a similar problem and if so can you please help out.
Cheers
Paul
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Hello Paul.
I have a 1999 Focus 1800 Zetec manual estate and had exactly the same problem in 2003 after 34,000 miles. The problem was then cured by cleaning the "throttle body and idle control valve". This after a mobile computer diagnostics check revealed no engine management fault.
However, the problem has now reappeared at 48,000 miles and the above cleaning has again been carried out by a different garage. They say that whilst cleaning may cure the problem, the underlying cause has something to do with a malfunction of the air conditioning switch which should make some revs adjustment when turned on.
The above cleaning was carried out today and I will know in a few days whether it has been successful again.
I should also mention that both the above situations have been preceded for a time by what feels to be a reluctance for the revs to reduce when taking the foot off the accelerator to change gear.
Any comments on the above by anyone having the same problem would be appreciated.
Thank you.
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