Disc valve on transmission operation?
 

I'm getting a P0121 Coolant performance code.

Various Rennlists direct me to the disc valve on the transmission being problematic. I've confirmed the valve is not damaged, the temp sensor is working and I have good vacuum.

I do notice the valve isn't closing on idle or when the transmission in a cold state. I'd assume the valve would be shut and not allow coolant to circulate through the transmission cooler until a hot state.

Can someone confirm the valve should move to a closed state when the engine is idling?

Thanks

An update for future references:

- I've confirmed the valve should move and be in a closed state when the engine is idling.

- Turns out I had a partial vacuum leak coming from a small nipple which is attached to a main-line-vacuum source. Since this is right next to the limited-slip cover, I suspect it can get damage easily if there is LSD work.