my bmw e46 3 series wont start and when it will it wont stay started for long. Help!

i brought a bmw E46 1.8 saloon a couple months back and when i first had
it it would every now and then cut out randomly. this problem got worse and
worse until the point i had to take it to my local garage, they said it had to
be the air flow meter so they tryed changing it  but it did nothing to help the
car, they couldnt figure out what else it could be but when they tock the
plug for the airflow meter out the car and it ran like a dream
so they gave me the car back with the air flow meter unplugged,  they told
me to go to a bmw specialist because i may need an original bmw air flow
meter.
but i drove the car around for a coupe weeks anyway or though the meter
was unplugged and there wasnt any major problems except it not starting
every now and then until it cut out on my way to work and now it just wont
start unless i leave it 12 hours or so and even then it will only run for about
5 minutes,  ive tryed changing the filters and made sure its not any thing to
do with the fuses, i can hear the fuel pump working but but the car just wont
switch over. its a really good car onces its running but i just cant fix this one
problem thats messing the car up. so does anyone have any idea on what
would be a good next move?