Learn Spanish (Latin America): Me tambaleaba cuando la cuerda se rompió; ¡por poco y caigo! - I was wobbling when the rope broke; I almost fell!

This is a special rule for por poco (almost). When narrating a past event that almost happened but was avoided (a "close call"), Spanish speakers frequently use the present indicative (caigo) instead of a past tense. It makes the near-miss feel more vivid and dramatic.

What does the y do in por poco y caigo? Can I leave it out?

You can definitely leave it out. Por poco caigo means exactly the same thing. Adding the y is just a common colloquial habit in many parts of Latin America that makes the phrase flow more naturally in spoken Spanish, but it adds no extra meaning.

Why does this sentence use both the imperfect (me tambaleaba) and the preterite (se rompió)?

This is a classic example of an interrupting action. The imperfect me tambaleaba (I was wobbling) sets the background scene for an action that was already ongoing. The preterite se rompió (broke) is the sudden, completed event that happened in the middle of that background action.

Why is it se rompió instead of just rompió?