As** Just Asking Questions** implied, The Enemy Below, with Robert Mitchum as Kirk. The plot item about the Romulan holding a course for home comes straight from the movie. The ending is different.
They have said “all stop” and “full stop” at times. Both are directions to stop the engines, the latter meaning, do it fast, or we’ll fucking hit a de-cloaking Romulan warbird!
As with all things Star Trek, this isn’t always true. Depends who was writing that day. At least one episode for sure, they run up through warp .5… .7… .8 etc.
Just as, for every 10 episodes where the Enterprise is obviously hovering over the landing party, ready to blast something into oblivion with its phasers, there is a Mirror, Mirror where the Enterprise is seen orbiting out of phaser range as a plot point.