I have a 2015 polaris rager that quits now and then and a 520305 code comes up, what is wrong. throttle body has been changed?

When it does not start spray come starter fluid into the throttle body/carb to see if it will run. If so, it is a fuel problem. Also check electrical connections for looseness.
Possible contamination of the fuel with water.

Odds are your carb needs to be taken apart, cleaned, reassembled and adjusted if needed.

Spray some starter fluid into the throttle body. If it starts then it is a fuel problem. Check the fuses for injection operations.

Here is a video that might help. https://www.youtube.com/watch?v=3rhe2BzIOLA

try resetting codes by removing both battery cables then touch them together away from battery terminals. then reconnect cables and start to see if it has same codes. not a valid code according to polaris code list

"Throttle Body Control - Adaptation Aborted, Condition Exists"
Output of your ETC Throttle (Electronic Throttle Control) is out of range, possibly a bad connection from the Throttle Body to the Electronic Control Unit

P16A8 This Trouble Code sets if the Injector Output Supply 2 Voltage is below an acceptable limit. Can be caused by Damaged Wiring or Faulty/Shorted Connectors.
ECU Output Supply Voltage

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sounds like your high jet in the carb is either clogged or you have water in your fuel.

you will have to have a nulti meter and unplug the sensor and che the ohms on the sensor when you move the control, it should move up and down on the ohm numbers smoothly if jumps as you apply throttle then you have a bad sensor