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

Now, there may have been reasons why Buddy acted up.

From Literature

I listen for a whistle when she inhales, a sign her asthma is acting up, but don’t hear one.

From Literature

“This is my insulin pump. It’s been acting up the past two days.”

From Literature

A couple of years ago, a falling durian landed on his shoulder, leaving him with a throbbing pain that acts up now and then.

From BBC

“The smoke and ash made my asthma act up and I couldn’t breathe.”

From Literature