They didn't give me a reason and it wasn't until after I had it replaced that I suspected they just threw it on there to make themselves money. I replaced the valve and got an engine code for it. Turns out the part I bought was faulty. I replaced it and the code didn't come back. But I thought it was suspicious that I didn't have a code for it before when they told me to replace it. Their quote for it was almost $400 for the part itself and almost $200 for labor. I got the valve myself for less than $100 and it took five minutes to put in. Lesson learned!
I'll look into cleaning the TB this afternoon and see if it helps. I had the IAC valve written down as a maybe but I wasn't sure because it said something about stalling while decelerating - mine is always during standstill.

I know it probably had nothing to do with it but I replaced the thermostat yesterday. I stalled on my way out of the gas station later that day though. I ran the cleaner through a while ago actually just before I took a two hour drive to Delaware.

Thank you guys so much for the suggestions. I'll post an update on if they work. I have my fingers crossed!