That is exactly whats giving me hell right now with my Q45 TB.
I can't for the life of me get it to idle correctly. If I adjust the idle to where it will stay running while cold, when it warms up, it won't idle. If I adjust the idle while warm, it dies when cold. I just now noticed that water pipe thermostat circuit used for idle adjustment while cold/hot. Problem is, I deleted the OEM water lines that I could have used to feed the warm up circuit on the TB.
Has anybody went ahead and removed that warm up circuit lever from the TB ? It will come right off with the removal of its retaining bracket. Then, there would be nothing to alter the idle on the TB except the idle screw.
I think whats happening now on my set up is, I don't have hot water flowing thru the TB to activate the fast idle thermostat circuit, but I think even though, the engine bay heat, with heat soak is heating up that thermostat enough to raise and lower the idle anyways. Thats why I can't keep a steady idle lever position. Its getting enough heat soak to operate the lever plunger, even though no hot water is connected.
I need to remove all of the water controlled idle components, so it will at least not have that variable to deal with....
Anyone delt with this before??