2012 Hyundai Sonata GLS automatic 59251 miles. OBDII ...TP(%) 14.5 at idle. It's that high? It's my throttle position stuck or broken and would that cause inefficient gas mileage (15 street and 25hwy)?
It's my throttle position stuck
if it was stuck you probably wouldn't be able to go anywhere.
Press the accelerator and see if the value changes.
For tips on how to improve fuel economy see our FAQ.
TP (Throttle Position) is just a reading from the throttle position sensor. You need to research what the normal idle reading should be for your car before coming to the conclusion that you have a problem. Have you tested your throttle position sensor? Are there any symptoms other than perceived low gas mileage?
Depending on the kind of driving you do and the engine the car is equipped with (that model offered a turbo and hybrid as well as normally aspirated 4-cylinder) your gas mileage may be what would be expected under those conditions. See the FAQ for information on fuel economy issues.
There is also a free online repair manual at charm.li that may help:
https://charm.li/Hyundai/2012/
