Preheat a 6-quart Instant Pot using the saute setting on high.
Add 2 tablespoons oil to the pot and brown your turkey pieces in batches, adding more oil as needed, until golden brown on all sides, 3 to 5 minutes per side.
Add all the browned turkey pieces back to the pot along with the garlic, celery, carrot, onion, sage, bay leaves, rosemary, thyme, peppercorns, 2 quarts water and 2 teaspoons salt.
Lock cover and set to pressure cook on high 45 minutes. After cook time has finished use the quick release button to release all steam. Strain the stock through a fine mesh strainer and skim any fat off the top before using.