This model has the dual-point ignition.  Be sure that they are BOTH set
correctly and that the sensor to switch them after warm-up is hooked up and
functioning correctly.  I seem to recall that Mirafiori.com has a good FAQ
on this system, or check the Haynes manual for the procedure.  It's also
worth checking to make sure a prior owner hasn't "fixed" a clogged idle jet
by cranking down on the throttle stop.  My stock '78 idles great hot or
cold, so it's shouldn't be a design issue, although there is an awful lot of
emissions plumbing on that car, so there could be a cracked or misconnected
hose or stuck valve somewhere.

Al