RichThesaurus
throw a spanner in the works
vs
throw a spanner into the works
throw a spanner in the works
verb
To introduce a problem, dilemma or obstacle, something unexpected or troublesome.
throw a spanner into the works
How often have the words
throw a spanner in the works
and
throw a spanner into the works
occurred in a corpus of books?
(source:
Google Ngram Viewer
)