Combine the potatoes, poblano, salsa, cilantro and 3/4 cup water in a 6- to 8-quart slow cooker. Tear the tortillas into small pieces and stir into the mixture. Cut the pork in half and season with 3/4 teaspoon salt and a few grinds of pepper. Rub all over with the cumin and coriander. Add the pork to the slow cooker. Cover and cook on low until tender, 7 hours.
Remove the pork to a plate. Stir the corn into the slow cooker and cover. Shred the pork into bite-size pieces, discarding any large pieces of fat. Return the pork to the slow cooker; season with salt and pepper.
Divide the stew among bowls and top with the sour cream, pickled jalapenos and more cilantro. Serve with warmed tortillas.