My 08 sierra was showing error code 0121 throttle position sensor. I took off the throttle cleaned it with TBC and purchased a new throttle position senson and put that on. Started the truck and it will rev to 3000RPM sometimes and not come back down. Other times it will go up to 1.5 and stay there enough to get it into gear but when driving and stopped at lights its up at 1000RPM enough that you have to be heavy on the brakes. Did i miss a step after installing the new throttle position sensor?

 

Need to hook up scan tool and do idle learn