2010 Expedition EL Flex Fuel 4WD. 42K miles. I'm the second owner. Have the extended warranty and it is good for a while (5 yr / 100K miles IIRC).

As in my previous thread on the subject....

First start/cold start, the vehicle either wont start or will start but will be on the verge of stalling out. Dark smoke out of the exhaust. There are some times when it will take a couple of minutes of trying before the truck will start and run. Once it stays running (30 sec - 1 minute or so), it runs smooth and normal and has no further issues. I don't know if it's a coincidence but the wife (it's her truck) says that she noticed that it does it mostly when the fuel is at or below 1/2 tank and when full doesn't seem to do it. I have not been able to test this theory so I can neither confirm nor deny.

The first thing I tried was changing the fuel filter. I have been unable to find a manual at my local parts store but I figured how hard could it be? Well, apparently the Flex Fuel model has a "Lifetime" fuel filter that is located inside the fuel tank. So much for that idea.

I took it to the local dealer and they did a computer reset as that is a common fix to the problem I've described. No dice. Still doing it.

Took it back, parked it overnight and they put the diagnostic computer on it prior to starting. When they tried to start it, same problem. They apparently ran the tests on it and found nothing.

I spoke with the service manager, in essence, the explanation was "sometimes they do that". The service manager said that they got no error codes from the diagnosis so there's nothing more to do. WTFO? Instead of defering to the little magic box, how's about doing some o that mechanic stuff slick.

I'm no mechanic but I know just enough to either keep me out of trouble or get me into trouble depending on the circumstances. Dark smoke when difficult to start tells me unburnt fuel coming out of the tail pipe. That tells me either poor ignition or excessively rich mixture. Am I missing anything there?

I made a few phone calls and got one suggestion from someone who's seen this before (not a mechanic though). In those cases it turned out to be either an "Idle Air Control Valve" or "Air Bypass Valve" malfunction or failure. Both of those things sound suspiciously like something that would effect the fuel/air mixture. In addition, both of those things will NOT show up as any codes and they are both covered by the warranty.

If anyone has any comments, suggestions or like experiences...I'd be happy to hear from you.