The car is a: Ford Focus 1.8LX petrol
2000 X reg 103,000 milesIt was last serviced about 6,000 miles ago and is generally running fine apart from the problem I will try to describe below.
Occasionally, when it has not fully warmed up, but isn't freezing cold, it will rev by iteslf, ie with no pressure on the accellerator pedal it will hold the engine speed at about 3,500 revs.
I would suspect that the throttle cable was sticking if it wasn't that occasionally it does something really strange whereby (again with no pressure on the pedal) the revs will drop down to the normal tickover speed and then slowly pick up to about 3000 revs and then drop down again and this will repeat roughly every 5 secs.
To stop either of these problems, all I need to do is blip the throttle so that it picks up to about 5,000 revs and then it's fine. It will occasionally do it again on a journey but has never done it when fully warmed up.
Has anyone seen anything like this or have any idea where to start looking?
Many thanks in advance for any help.
Mike