slow down vs throw a spanner in the works

slow down

verb
  • To reduce the velocity, speed, or tempo of something. 

  • To decelerate. 

throw a spanner in the works

verb
  • To introduce a problem, dilemma or obstacle, something unexpected or troublesome. 

How often have the words slow down and throw a spanner in the works occurred in a corpus of books? (source: Google Ngram Viewer )