When starting truck up in the morning it idels high , after it warms up the idels goes back down service engine light comes on .I get a code 43 .What is the problem

Trouble code doses not indicate ANY PART has failed! ... This code could be caused by engine noise or vibration - I have worked in the auto repair business a very long time - have never had a failed GM knock sensor - code was always generated from another source. Idle air control valve likely culprit for excessively high idle rpm - possibly vacuum leak. Good luck!