will start then dies when not hold foot on gas
There is a Fuel Injection Idle Air Control Valve that may be bad.
Also might just check around for loose or disconnected vacuum lines just in case. They are usually rubber or plastic hoses that mostly lead to the intake manifold. Sometimes they get old and dry rot or deteriorate from heat/oil. Bad hoses can be replaced for cheap. Also check for the smell of gas, as a fuel line or regulator may be leaking and causing a loss of fuel pressure. Or you just may need a tune up with new spark plugs. The IAC may very well be the culprit so just try the simplest things first. If the vacuum and fuel lines are good, you're sure your plugs are fine, and and the IAC tests fine, I would then look at testing the fuel pump.
My mom has an 1994 expedition and also dies down when she drives it down the road
Tell your mom to get it into a shop for repair before you get stranded somewhere.
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