asking on behalf of a mate

I own a 99 Ford Fiesta and basically i have an intermittent fault which is freaking annoying. Basically when coming upto junctions the car will stall, some days it happens 2/3 times a journey other days it doesnt happen at all.

Now ive taken to it 3 garages, the last one was a Ford garage and no-one can seem to fix this.

I've had the follow parts changed/fixed:
Breather Hose
Idle Control Valve
Gear Sensor
Spark Plugs Checked
Battery Checked