I've an idling problem with my '99 focus, sometimes it cuts out when coming to a halt, sometimes the idle is erratic, sometimes (rarely now) it's ok. The weird thing is that if I switch the heated screen and rear window on it's ok. Any pointers anyone please?

It's a common problem on them. Idle Control Valve gets sticky and needs cleaning up or worse case replaced. Though it does sometimes have an ecu issue as well IIRC.

Can you here a whooshing noise from the engine?

Look under the throttle body theres a breather pipe that goes from the naifold round to a metal pipe on the gearbox side of the engine,. These perish and suck in causing the problem you describe. It goes to the idle control valve. Common as muck and the dealers keep them 8 quid iirc. Iv fitted loads.

I would agree with dan. Air leak also look on the back of the manifold at all the pipe work.

Have a look here it shows locations ect

http://www.btinternet.com/~madmole/Page.html

look at the bad idle guide.

[Edited on 5/3/10 by big_wasa]

Thanks folks, I'll investigate.

A failing speed sensor can also cause this problem and is quite a common focus fault. Have you ever noticed the speedo stop working briefly?

[Edited on 5/3/10 by MikeRJ]

No, the speedo seems ok. If I dip the clutch at 50 and run down to a stop the speedo comes down ok , it idles ok all the way down to about 5 mph then plays up.