My car does this as well, but I'm having some weird problems that would take a long time to explain. Anyways, it does this when it's hot, and it's been doing its poopy running thing. Do you hear your fuel pump going? I do. I have power but no crank.... Soooo what I do, is open the hood, reach into that Bavarian Bay, on the drivers side at the firewall, and look for the Solenoid (at least that's what I think it is... I haven't looked it up yet... ) there's three wires on it (I think) look for the one that attaches to a blade tip (lower one).... I take the wire off, shake it around a bit.. then put it back on.. Usually starts right up... (I think mine has a bit of corrosion on it, haven't gotten around to cleaning it.) Anyways, that's what I do... And if anything, you can always short the terminals together with the screwdriver from the tool kit... (I don't know if that hurts the car or anything.) Good luck, hope this helps a little.
Drive on, Bimmerheads.
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