Audi

My 2002 audi a4 began to get hard to start then this seemed to progress into it missing a bit and being slightly underpowered. It then put up the engine managment light and Ecs light. I took it to my mechanic who said it was showing a crank shaft senor fault he replaced it.I lifted my car tonight and it seemed to go fine but then as I drove a few mile it started to miss again.I went to a petrol station filled it with super unleaded and put cleaner in it fearing I mite have got bad petrol somewere when I came out the car wouldnt start it just kept turing as if it was getting no petrol. I give the car a push it started with me bump starting it, I continued on home car still missing and stopped the car then when I started it again the two warning lights came back on and the car was running at a slighly higher rev than normal.I am completely beat with this problem and dont know what to do!