If you have your original TB I would put that one back and see if it fixes you problem. You also need to read the trouble codes causing the wrench light. That will tell you if you TB is bad.I have a 6 speed 2014 mustang v6, and kind of have the same problem!!! When I am at a complete stop like stop my car idles weird it sets at 600k rpms then goes up to 1000k rpms then goes back to 6 and back to 1k & etc. my car also has also been like bogging in a way when I'm driving it sucks lol. I just recently got the wrench light on my gauge cluster, I did alot of research and I'm figuring its my throttle body that's causing this problem. I have a 73mm bbk throttle body and have a quick question should I just buy a new one? like that is all I can think about lmk if you ever fixed your problem , thanks !