temperamental

(a) relating to or caused by temperament
- temperamental indifference to neatness
- temperamental peculiarities
(s) subject to sharply varying moods
- a temperamental opera singer
moody,
(s) likely to perform unpredictably
- erratic winds are the bane of a sailor
- a temperamental motor; sometimes it would start and sometimes it wouldn't
- that beautiful but temperamental instrument the flute - Osbert Lancaster
erratic,

moody erratic

temperamentally