Question

On my 2007 Chevrolet Suburban 5.3L I have the code P0121 and P0300, clean throttle body reset ECM code came back

Answer 1

P0121 Throttle position (TP) sensor 1 performance

P0300 Random misfire

The random misfire is the condition you will have to satisfy first, this can be from ignition problem , to low fuel pressure . P0121 is a type B code condition which can not cause a random misfire, When P0121 occurs it is when the MAP (manifold absolute pressure) sensor is outside the calibrated range, It is the misfire condition that has to be done first.

Answer 2

P0121 CHEVROLET Code - Throttle Position Sensor 1 Performance
Read more: https://www.autocodes.com/p0121_chevrolet.html