just bought a focus with a zetec 1.8 in it when i stop at a junction the engine cuts out and every now and then the speedo cuts out,do you think it might be the speed sensor.also when you put the ignition on the speedo and rev countr go all the way over then back down

 

NO won't be speed sensor as it does it when stationary, try cleaning the ISCV, have a look at the rear of the underside of corner of head, where the pipe from the front mounted PCV valve meets the "T" piece, well known for perishing, causing air leak and weak mixture.
Clean the MAF, with carb cleaner, then reset KAM fuse in fusebox, a violet 2 amp one.
tabetha

 

will try that in the morning thanks

 

It will be the speed sensor thats causing your speedo to work intermittently, they always fail, very common.

The engine cutting out when pulling up to a stop is probably the idle control valve, you can try cleaning it out but if it were me I'd just bang a new one on.

And the focus doesn't have this T-piece either.

 

defo the speed sensor, mine was doing the same and fixed it

 

Would also say speed sensor. Is your EML on? Does car idle ok when cold if so ISCV must be ok as this only operates on a cold start or when a load is placed on engine such as electrical equipment. Easiest way to tell is to unplug and go for a drive and see if there is any change.

Martin