Volvo: 1984 Wagon Not Starting, type of corrosion, little sand

Question
 My 1984 Wagon does not start sometimes.  It turns over but
does not start.  It is completely intermittant.  Sometimes, if I
come back a few hours later, it starts right up.  The garage had
it for a week and it started everytime.  It seems to have spark
and fuel.

Answer
I had a problem exactly like this a few years ago on my 80.  I found it to be corrosion on the 12V terminals on the coil.  All it took was a little sand paper to the contacts to clean them up.  Given that, I would do a careful once over of your electrical system from the coil to the plugs looking for that type of corrosion or condensation.  Sandpaper all the contacts that look questionable.  Good luck!