Preheat oven to 350 degrees. Spread pecans on a rimmed baking sheet; bake until lightly browned, 5 to 7 minutes. Set toasted pecans aside to cool.
In a medium bowl, whisk together sour cream, vinegar, and sugar until smooth.
Add celery and apple; season with salt and pepper. Toss gently to combine. Crumble toasted pecans on top, and serve immediately.