I have seen this twice on B2xx engines, both times I think it was an
intermittent head gasket leak.  The logevity of the Engines combined with
lack of corrosion inhibitor in the coolant can cause an intermittent channel
between cylinder and cooling system.

Water gradually leaks in under certain conditions (temp / standing time) and
then seals up when the engine starts, the plug is wet and won't  spark until
it dries a little.

If you leave it too long it can form a larger leak which intermittently
dumps the entire coolant into the cylinder under the induction stroke and
the engine will overheat very quickly.

I would advise that I am guessing a little, and am in the process of doing
this on my 940 Turbo, although it also had other problems, it did have this
symptom.  The fix is a head skim and new head gasket.

--
Tony Stanley