[Jadeh]

So I have owned this petro bmw for 14 months, its been great untill just before Christmas when it started going pear shaped.
It had a miss fire on cylinder 4, took it to a bmw specialist and he said I had a faulty injector so he replaced the injector and all 4 plugs.
Swapped the oil and oil filter as he said it had been contaminated and gave me the car back.
All was fine until a month later when it started playing up again.
Back to the garage and this time he said the faulty injector had killed the nox sensor and so he changed the nox sensor .
Again all was good but this time only lasted 1 day.
Took it back AGAIN and it smelt eggy and ran like crap, so he de sulpherised it and did something on a computer.
I picked the car up yesterday as he was shutting an I could tell within 2 minutes it wasn't right.
So I took the car home and got a neighbour to plug his computer into car to see what it said.
The codes it gave are
0030702 cylinder balancing
003104 uneven running stratified charge
002af8 nox sensor linearly shear test
0029cf miss fire cylinder 3
0029d9 miss fire at low level tank

I've already spent £1000 and its making me feel like crying.I really don't no what to do its only done 55k miles and its a lovely car but it's really getting me down.
Any help or advice would be really appreciated