Bring potatoes and vinegar to a boil in a medium saucepan (vinegar should cover potatoes). Reduce heat to medium-low, and simmer potatoes until just fork tender, about 5 minutes. Let potatoes cool in vinegar for 30 minutes. Drain well, and gently toss with oil, salt, and pepper. Preheat grill to medium-high. Grill potatoes in a single layer until browned on both sides and cooked through, about 5 minutes per side. Sprinkle with salt before serving.