I've got an intermittent problem with my 1996 Brava which I'm trying to
pinpoint.  Here's what happens:

I can drive the car normally for about 30 - 40 minutes with no problems at
all.  But when I stop at a junction then pull away again the engine will
rev but there'll be no drive unless I let the accelerator out a bit at
which point the engine picks up again.  If I then stab the accelerator
again the engine will rev but no drive unless I let the accelerator out a
bit again.  This will go on for about 10 minutes at most and then the car
will return to normal.  Sometimes it will do it for a couple of seconds
after I've been in the car for about 10 minutes but I can almost guarantee
that it will happen at 30 - 40 minutes into my journey when I pull away
from a junction.  In fact there's one stretch of road that I drive along
at 35 minutes into a journey that it will always do it on!  There's no
strange noises when it does this.  Everything else seems to be ok on the
car although I did notice the temperature gauge needle jumping around
erratically when I'd stopped at a level crossing earlier.  Also, about 3
months ago the fuel injection warning light came on about 3 times in one
week but that hasn't happened since.

I've tried to make the clutch slip to see if that was the problem but that
seems to be ok, at least when the car is running normally.  It doesn't
lose drive when I'm driving the car at a steady speed.  It seems that the
trigger for the problem is when I pull away from a junction and go up the
gears and only within that 30 - 40 minute window and even then only last
for about 10 minutes at most.  

Anyone got any ideas as to what it could be? :)