Thanks for coming to Just Answer, if I could get some more information about your sister's Taurus, when it stalls, does it restart right away or does it crank but not start, and does she have to wait to get it restarted ? Also, has the check engine light ever come on ? Thanks, Brian.
It starts right away. Only happens at stop signs or red lights. Mechanics keep telling her "Oh. Fords do that."
Also, thye tell her they won't work on it b/c it a DOHC. She's 72, on fixed income and is spending money she can't afford.
The things you mentioned are very good possibilies, the idle air control valve is a very common thing to cause this concern, however this will not usually leave a fault code in the computer. A vacuum leak is also very common in this engine, a couple of areas you can look at are the two hoses that come off of the valve covers and go into the air intake hose, follow these hoses from the air intake hose, this is the large diameter hose that comes from the air filter housing to the throttle body, at the point where these hoses attatch to the valve covers are an elbow, one at each valve cover, this elbow is rubber and over time deteriorates and become soft, it will sometimes collapse or develop a hole in it, this will cause the stall, check both of these elbows. Another hose is the hose that attatches to the underside of the throttle body, it is a larger elbow that supplies vacuum to the pcv valve, this will fail in the same way, if all of these hoses are ok, not leaking or split or collapsed, I would replace the idle air control valve, also, clean the inside of the throttle body around the throttle plate with a shop rag soaked with carb cleaner.
Thank you very much for the details you provided. Knowing that the IAC may not trigger a fault code explains a lot. Further, you've provided me with the information I need to track the vacuum hoses and see about getting them checked/replaced for her..
Let me know what you find or if you need more info, as I will be glad to help.