Experienced advice needed Please!
I recently bought a used Expedition with the 5.4. It has intermittently run very roughly and will not maintain an idle uless you apply extra throttle. It goes into this bad running mode intermittently, runs fine for a few days or even three weeks, then bad idling again for a few short trips.
I'm afraid to let my wife drive it as when it fails you stall when cornering with your foot off the gas, the power steering becomes VERY heavy and a safety concern.
I had autozone check the codes after the last failure, it cleared up 2 miles before I arrived at Autozone, they found no stored codes. I bought a Code Scanner to have ready and waited 7 days, this morning it finally failed again and I was ready. Unfortunately it finds no codes! I drove 15 minutes to work, rough running and wanting to stall at every light all with no codes found.
It feels like one or even two cylinders not firing. When it is not in this failed mode, the truck runs perfectly and gets 18 MPG highway.
How should I proceed? Can a mechanic find the problem with no codes and this very intermitetnt behavior? Right now it is in failed mode but by history will clear up probably after a few more miles. Warmup?

Any help much appreciated, thank you.

 

Bad coil pack(s) possibly.

 

Sounds like a loose plug maybe. Maybe a sticking IAC valve>??? Bad injector maybe. Does anything else act up or does the motor just run bad>??? -Mat-

 

No, nothing else acts up, just the rough running. When you give it some throttle it seems OK, maybe a little rough or low on power but not too bad, but it won't idle.

Any better method than trial and error through those possibilities? I had high hope for help from the codes, no code is a great disappointment.

Thanks.

 

i would think start with cleaning the iac. easy to do and doesnt cost anything.

 

I'd check the plugs.

 

I'm thinking IAC too possibly. They are notoriously problematic on some Fords. My Mustang had the same idling problem.

A good way to check is to pop the hood and give the IAC a tap with a hammer or something while it is idling badly. That should free up the valve and correct the idle. FYI, the IAC is a silverish, cylinder looking thing, near the throttle body.

If indeed you find that is the problem, you can try cleaning it, but you're probably better off replacing it.

 

If you can catch it doing it in the driveway, unplug each coilpack and replug. If you come across one that doesn't make it run any rougher, there ya go. That pack is going bad. Incidently, I was looking at mine with an SVT tech who had his computer hooked up to it. He unplugged one to make it misfire and it didn't even through a code . Anyway just some info. Hope this helps.

BD