i have an e36- similar problem- everytime i turned a corner- or brakd- or slowed down etc etc- the engine would cut out- the power steering would turn off and i would be left fighting with the wheel to gain some control- but the engine would always restart -
when driving it was fine
i was told it was a big big job by someone at bmw.
a week later- my local mechanic told me it was an air hose- going to the air box - quite a thick one- had a massive tear in it- replaced that �15- never happened again-
so check all the hoses- this particular hole was just a thin slice straight down the side and i and numerous others never even noticed it-
maybe worth a look if youre still having the problem.