My mate has a 2001 focus (1.8) petrol.

He says that the engine dies at low rev's even when driving and changes gear it cuts out.

I'm going to see him today so was wondering if you guys had any ideas?

I can think of the easy bits air filter, fuel filter or fuel pump but just wondering if i'm missing some thing obvious.

YQUSTA

idle speed control valve could cause it as could an air leak,check the pipes coming off the inlet manifold,especially the one going to the crankcase breather they have a tendancy to suck in and split.only other thing i can think of as you have no diagnostic eq  to aid you is the throttle postion sensor or its voltage out of range.try loosening it push the throttle a few times and do it back up.something to start you off............

Cheers jonesier will give it a go

YQUSTA

mine was the same idle control valve was FUBARD. Mine's a 2000 1.8!

Worth checking all the plug leads are seated OK.

As mentioned by jonesier1, there's a rubber hose from the rear of the inlet manifold (quite a long way down) which is known to go soft/gooey, split and basically is a pile of poo.
This joins up with a metal pipe which goes under the thermostat housing then to the ccv/oil separator on the front of the block.
The whole lot of that, including the 1 way valve (the bit which pushes into the top of the oil separator), is worth replacing. Under £20 for all the parts and needs doing if it hasn't been since new.