Erratic can also mean "inconsistent" or "irregular". So a stock market that often changes direction is said to be acting erratically; an erratic heartbeat can be cause for concern; and if your car idles erratically it may mean that something's wrong with the spark-plug wiring.

What does erratically mean?

The adjective erratic describes things that are unpredictable, unusual, and that deviate from the norm. ... Like its linguistic relative, error, the adjective erratic means "deviating from the norm," or "wrong." It also implies behavior or qualities that are unpredictable or odd.

How do you use erratically in a sentence?