Occasional stumble at start and occasional thermo not registering

[Leah Mueller <muellerl@cadvision.com>]

Once stone cold, and once warmed up, my 86 4kq has started up just fine,
but then it did not want to idle unless I kept it going by gently feeding
it gas. If it died out, it again started fine, but stumbled.  Once I got
going, things seemed fine, exept a slight rough idle when warmed up. Also,
my temp gauge has a few times not registered any temp and then suddenly
came back to life.  Temp sender or air in system?  I have recently flushed
system and put in new coolant at 50 50 mix. Thanks for any ideas.

David
86 4kq with K&N filter.