Hi and thanks for using 2CarPros.com.
Based on your description (the headlights causing the engine to stall), leads me to believe there is a ground issue. As far as the IAC, it only maintains engine idle speed and does nothing once you open the throttle, so I do not think it is that component.
First, check to make sure the battery terminals are clean and tight. I would suggest removing them, cleaning them and then reinstalling them.
Here is a link that shows how to clean them:
https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked
Next, check the condition of the ground cable from the battery. Note that the main lead goes to the engine block. Confirm that it is in good condition, where it attaches is clean (not corroded), and the bolt is tight. If the cable is questionable, I would recommend replacing it. They are inexpensive. Additionally, often times there are smaller ground wires which come off the main one. They attach to the body of the vehicle. Same thing with them. Make sure they are in good condition, clean and tight.
I have attached a picture which indicates ground points under the hood of the vehicle. Inspect them and let me know what you find.
Hope this helps,
Joe
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Friday, July 27th, 2018 AT 9:49 PM