I have a 1990 M3 with 56k on the odometer. It is in very good shape and has the Turner 2.5 kit recently installed in it. However, it loves to shut down with seemingly no reason. It usually happens when downshifting from 3rd to 2nd. It'll be fine one moment and then...nothing. To get it going again I'll just depress the clutch and whoom, there it goes again...like nothing happened. It does this quite often and the dealer has found nothing wrong with it. And of course, when I take the service guy out to show him the problem, it won't do it!! Any advice would be appreciated.