Cool One's Jets Meaning

(idiomatic) To become less excited, intense, or active; to exercise self-restraint.

Example: 1999 April 7, Joyce Slaton, "Phantom Menace Book Tells All," Wired:
  Star Wars fans who positively can't cool their jets until the 19 May opening of Star Wars prequel The Phantom Menace need wait no longer than until early May.
2004 Oct. 6, Kirk Honeycutt, "Taxi (film review)," The Hollywood Reporter:
  Belle's boyfriend Jesse (Henry Simmons) is left to cool his jets while his woman bangs around the New York area.