Place potatoes into a pot and fill with enough water to cover. Bring to a boil and cook until potatoes are almost done but still firm, about 15 minutes. Drain and cool.
In a cup or small bowl, mix together the paprika, cayenne pepper, mustard powder, garlic, black pepper, celery salt, cumin and parsley. Set aside.
When the potatoes are cooled, slice them lengthwise into wedges. Place them skin side down on a plate. Coat with cooking spray and sprinkle the seasoning evenly over them. Cover and let stand for 1 hour.
Preheat an outdoor grill for medium heat.
Grill potato wedges until browned and hot, turning occasionally to avoid burning. Serve with sour cream.