Press SAUTE button and let the pot heat up. Add the oil to the bottom of the pot once it's heated.
Add in beef stew cubes, garlic salt and salt and pepper. Let the meat sear for 2-3 minutes or until the edges of the beef stew cubes start to brown.
Add in the onion, garlic clove, and fresh mushrooms. Mix it all together.
Add in flour and mix all together so everything is coated in flour.
Add in Worcestershire sauce and beef broth and stir.
Place lid on top of Instant Pot and turn valve to SEALING (not venting).
Press CANCEL to turn of the Saute, then press MANUAL (or PRESSURE COOK) and set timer for 12 minutes.
Do a QUICK RELEASE of the pressure and remove the lid once all the pressure is gone. Dump in the noodles (if you need more liquid, this is where you can add 1/4 cup - 1 cup of beef broth) and stir so that they are covered in liquid.
Place the lid back on top of the Instant Pot and turn the valve to SEALING.
Press MANUAL and set timer for 4 minutes.
Once it's done cooking do a QUICK RELEASE of the pressure. Remove the lid and add sour cream. Mix it in until meat and noodles are coated and creamy.
If your dish is too liquidy, press the SAUTE button and cook until the sauce thickens up.
Serve and enjoy!