Cook pasta in salted water until just shy of al dente, drain, rinse, and spread on a sheet to cool until warm to the touch.

Whisk the mayo, sour cream, mustard, vinegar, salt, and pepper into a smooth dressing.

Stir the warm pasta into the dressing until coated, then cool to room temperature.

Fold in the peas, celery, red onion, and dill. Serve right away or chill and stir again before spooning into bowls.