at infrequent intervals
at intervals
at odd times
at times
at various times
betweentimes
betweenwhiles
brokenly
by catches
by fits
by jerks
by skips
by snatches
disconnectedly
discontinuously
every so often
fitfully
haphazardly
here and there
in spots
infrequently
intermittently
irregularly
now and then
off and on
on divers occasions
on occasion
once and again
only occasionally
only when necessary
per saltum
periodically
randomly
skippingly
sometimes
sporadically
uncommonly
willy-nilly