run hot and cold

verb1

1. •
   To alternate between two opposite extremes, such as enthusiasm and disinterest or success and failure.

   • Henrietta's feelings for Delbert run hot and cold—one minute she's hopelessly in love with him, and the next she can't stand the sight of him.
   • The business runs hot and cold; some months our firm doesn't earn enough to cover expenses and other months, we net 400% profits.