I have a 1999 Ford Expedition. I was having trouble with it idling and now it won't start. What can cause this problem? Yesterday I was driving and had to double foot it to keep it idling. Every time I let off the gas the engine would die. It would take a minute for it to restart but it would fire up and run rough. I have not had problems like this until yesterday.
I have seen this in another Ford Expedition. Did the Check engine light come on, or has it been on for some time? Did your idle seem to be high occasionally in the recent past?
With this limited information it sounds like a large vacuum leak that the computer has been able to compensate for until it got so bad that it could no longer keep up. Once the vacuum leak has gotten big enough, the engine shuts off at idle, is hard to restart, and when it gets even larger, it allows too much air in and the engine cannot get enough fuel to start when it is cold, because when cold, it needs even more fuel to run properly.
There is a rubber and plastic hose combination that deteriorates over time and especially if there has been any oil leaking on it. It is at the rear of the engine, on the passenger side, and it connects to the intake and the breather hose going to the valve cover. I believe it also goes to one other place, but I cannot remember where.
To help find it you could get a can of carburetor cleaner, have someone attempt to start the vehicle while you spray in the aforementioned area. If it starts, stop spraying and you will probably hear a sucking sound. You can use the carb cleaner to more closely locate the leak by spraying puffs of cleaner and when you hit the leak the engine will rev up and/or smooth out. Look where you sprayed and you will find the leak.
ONE WORD OF CAUTION: do not douse the engine in carb cleaner. If there is a leaking spark plug boot it could ignite. Keep a fire extinguisher nearby and use caution.
I hope this is the issue and that you find it. Happy hunting!