Air flow meter

Hi, 2 months ago I bought an audi a3 1.6 SE, 1996, 68000 milage. When I bought it I could not take it away there and then because the man said the car is miss-fireing. So 3 days later, I picked it up and away I went. Only I noticed that when I set of it would take about 3 seconds for the power to kick in. It got really bad, so I took it back to the car sales where I got it from. He gave me a 3 months warranty when I got it. So I was told that the diagnostic said the air flow meter needed changing. I booked the car into a garage where they specialise in the injection. It cost me £160. When I got the car back, I noticed that something wasn't right. When I set off the revs would cut out and my battery would start to flash. I took it back and they said they tightened something up. I got it back and once again it would start to cut out. Then they said the air flow meter they put in was faulty. So they changed the air flow meter for the second time. I went to collect it, and once again it started to cut out only this time the car would totally stall. Its in the garage now and they have no idea what is wrong with it. They said they have to go thought the car manually. I don't want to be messed around by this garage anymore, have you any idea what coud be wrong with it so I don't get anymore lies off them. It never stalled before it went into the garage so in my eyes they have done something to trigger it off. :Evil: