Ford Escort engine idle problems

i have got 2 of these escorts m reg and n reg, on BOTH cars whenever the car is driving no matter what speed, hot or cold the car will cut out, the engine stalls and the the ignition lights are on, obviously if the car is rolling then you can bump start the engine and it starts but as soon as you put your foot on the clutch shock horror it cuts out,very rarely the revs drop down to 50 rpm and it stays alive, the only way i can drive is to knock it into neutral left foot brake and keep the revs up, a local garage put a flush through the engine? it and it was ok for a couple of days but back to square 1 again..... please help somebody!!! as i sais it happens on BOTH cars!!