act up

British  

verb

1. informal (intr, adverb) to behave in a troublesome way

   the engine began to act up when we were miles from anywhere

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act up Idioms  

1. Misbehave. For example, With an inexperienced rider, this horse always acts up . [c. 1900]

2. Malfunction, as in I'm not sure what's wrong with my car, but the transmission is acting up . In both usages up means “abnormally.”

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Example Sentences

On the morning of our departure, our van battery acts up and the motor won’t start.

From The Wall Street Journal

RCA still sees plenty of room for Sleep Token and its ilk to win freshly curious audiences, and conjure even more metal acts up the charts.

From Los Angeles Times

I started acting up simply to keep myself occupied.

From Los Angeles Times

I told her the camera is going to be constantly running, so when she’s acting up — and I wanted to open the film with that — she knew that was being recorded.

From Salon

“That’s not the idea. The idea is to have them clean their act up so that they do better and the stock goes up and their dividends go up,” Ryan said.

From Seattle Times