STVA/Throttle body concerns

I've got a 05 gsxr 750 I've just put 800 bucks into the transmission and now I've got it put back together it's throwing the STVA code 28 but only does it after idle for a few seconds (turn the switch off and then on again it shows c 00) crank it up then it idles smooth and then the idle changes and c 28 pops up again. Now the bike was tore down in my shop for like a month but I wouldn't think that had anything to do with that. Any suggestions? Or I have a whole throttle body off a 2017 gsxr 750 but don't exactly want to swap that from a running bike