E34 '89 525i (M20) cold weather problems

[Andy Stevens <andy@xxxxxxxxxxxxxxxxxx>]

I've got two weird cold weather problems with my 525i which may or may
not be related.

About 2 years ago, it started stuttering during the first few miles of
driving when the temperature was below freezing.  It can be going along
quite nicely at about 2000rpm, 50mph then the engine dies for a fraction
of a second, then back to normal.  After about 5 miles the problem goes
away for the rest of the day even though the car gets cold again at
work.  It's gradually getting worse with each winter.
Doesn't seem to be rpm related (can drop to a lower gear and it still
happens).  There's a blip on the tacho but otherwise the instruments
stay normal.

Second problem has started this winter.  It's now difficult to start
when cold (again roughly below freezing).  It catches on the first few
tries then dies.  If I then give it some throttle it eventually goes but
it's like half of the cylinders aren't firing for a few seconds.  It
often stalls again before I get out of the garage.  Again, once it's
running ok, the problem doesn't come back for the rest of the day.

So far I have changed the ECU (it just died last year), crank position
sensor and fuel pump relay, but the problems remain.

Any ideas of how to troubleshoot this anyone?

Thanks, Andy

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