Idle racing up and down on startup

[AHaase]

Hi All,
Was given a 2006 S80 2.5T AWD last year that had been sitting for a year and a half. Have been working through the issues, broken HVAC wire in dash, collapsed Nivomat, alarm controller unit and worst of all a trans valve body. Besides terrible gas mileage (around 17) I thought the car was finally ok when a couple weeks after the valve body replaced the engine started racing up and down on startup with CEL and note saying reduced power. Code was 925C throttle valve signal too high. Removed and cleaned the throttle body (was filthy with carbon and some oil) and made sure connectors were clean. Did not move butterfly when cleaning. Unit is modern Bosch type. Engine running nice and strong afterward but still having crazy idle about half the time when starting with same code and reduced performance. Alldata and Identifix are saying it could be a battery issue but battery is testing as very strong.
At a loss as to what to do next. Hate to buy a new Bosch Throttle body if not needed. Regretting giving my 96 850T to my daughter who loves it. Any help would be appreciated.
Thanks,
Andy

[aussieviking]

How did you check the codes? If you have DICE you can run the throttle body test.

Aftermarket code readers can be misleading at times, especially since you have the reliable throttle body type.

Have you checked all hoses for cracks / leaks?