corsa b, accelerate to start car

[supermoon69]

i have a corsa b 2000 (w reg)... envoy, i have had problems with it since ive had it like clutch etc. but everytime i want to start the car i have to press the accelerator otherwise it just keeps going and going and doesnt start,
tho once it is started it is perfect and doesnt cut out, because i had prolems with it cutting out when warm untill i changed the crankshaft sensor but now it is fine besides having to press the accelerator to start the thing,
any help please