Wiktionary
slow up
vb. (context idiomatic colloquial English) To slow, slow down, decelerate.
WordNet
Usage examples of "slow up".
It's sufficient to say that Sulu was drugged in order to slow up Kirk, should Kirk decide to leave suddenly.
Their purpose would be to slow up and misdirect the Posleen while military police backed by light armor would be rounding up, and in some cases driving, the refugees.
For the first time in their long alliance, Reggie was moved to bid Sam slow up.