Cook the rotini pasta according to package instructions. Drain and rinse with cold water to cool.
In a large bowl, combine peas, carrots, red onion, and cilantro.
In a separate bowl, whisk together sour cream, mayonnaise, ranch mix, milk, and lime juice to make the dressing.
Add cooked pasta to the veggie mix and pour the dressing over everything.
Toss well until fully coated. Season with salt and pepper to taste.
Refrigerate for at least 1 hour before serving for best flavor.