I have a 2002 F150 with the 5.4. It has been my wife's daily driver since inheriting it from my dad in 2013. Nearly two years ago it began stalling on her. First time was on the interstate while sitting in traffic. She had to push it to the side of the road and it restarted after a few minutes. I found nothing wrong and it was fine for a couple weeks. Then she was ready to leave for work and it started idling very rough and died. It would not restart. It threw a CEL and code for lean banks 1&2. I checked fuel pressure and found it would be fine and then all of a sudden drop, causing it to stall. I replaced the fuel pump and regulator and it ran fine for about a year. Then it did the same thing again.
Once again getting lean banks 1&2. Fuel pump was fine this time. I checked for vacuum leaks and replaced some suspect lines. No help. I pulled the intake and replaced gasket. Helped for a couple weeks. I replaced the MAF sensor and had no problems again for several months.
First cold spell this fall it happened again. So now I'm thinking its temp related and replaced the IAT sensor. No help. I found one of the vacuum lines I replaced earlier had worked itself about half way out. I added a hose clamp to it to better seal and hold it in place. Still no help. I got a code for heater circuit on O2 sensor. Replaced the O2 sensor and it was running fine again for a couple days. Then I was coming home as the sun was going down and temp dropping quickly. After several miles of highway driving it died at a stop sign. It did restart, and I was able to make it home, although it died at another stop sign and as I pulled into the driveway. No codes.
Any ideas?

 

The IAC valve may need to be cleaned or replaced. Pull the IAC valve and give it a good cleaning with throttle body or MAF cleaner. That may fix the problem. It's easy to pull and clean and makes a hell of a difference when clean. Check Youtube for F150 or 5.4 IAC cleaning and replacement videos.

If you want to buy a new one, get the Hitachi as it's original equipment, not the Motorcraft. Check the link..
https://www.rockauto.com/en/catalog/...ac)+valve,6072

 

Thanks for the suggestion. Can't believe I didn't think of there being an IAC. Thought they were more of a TBI specific part. But the sticking IAC does fit my symptoms.

 

So, I cleaned the AIC and there was a small improvement. I replaced the AIC and the symptoms were less severe, it would stumble, but not stall. For about a week. Now back to the same thing. Starts good, idles at about 1200 RPM, slowly drops. It seems like as it transitions from open loop to closed loop is when it happens. It will drop RPM quickly and then try to recover. I can't get a good read on fuel trim because it happens so fast, but I think it's going rich. Because it happens at the transition, I think its a sensor. But I have replaced almost everything.

Any more ideas?

 

Check the elbow on the back of the intake, opposite end of the PCV. It may look good, so remove it and verify it's not cracked or broken, it must be in good condition. Take a look at the EGR system too.

 

All vacuum lines have been inspected and replaced as necessary. Which was most of them. I was just thinking about the EGR. Another one of those things Ford makes hard to get to. I will try pulling it and cleaning this weekend. On the other hand, I might just go ahead and replace it so I don't have to do it twice. I hate throwing parts at this thing, but other than this problem, the truck has been good with just normal maintenance.

 

I haven't gotten to checking the EGR, been helping my son w/ his 66 Mustang. But it's a nice day today, about 60F, so I asked my wife to go out and start it to see what it does. Started right up and idles perfectly. Never a hint of stalling. I tried it a couple days ago in the morning, 40F and it acted up. So this is definitely temp related. Both temp sensors read the same, so it's not a bad temp sensor. What else could cause the stumble only when it's cold and switching from open loop to closed loop?

 

Checked the EGR yesterday. Pulled it off and cleaned it. Checked it with vacuum. It was fully open by 15in and closed smoothly from there to 0in.
It was warm, 65F, when I finished. It started and ran perfectly. Started it this morning, 37F, and it started right up but ran rough. Seemed to be rich, but I can't verify, I wasn't hooked up to watch fuel trim. Still obviously a temp issue.

 

Any more ideas? Because it only happens in colder temps, it has to be sensor related. Am I wrong? IAT reads correct. And coolant temps, both gauge and ECU, are correct and match. Are there any other sensors that are temp related?
How else can I diagnose this?
When it is running good at warm temps, all fuel trims are normal. When it's cold and stumbling, it seems to bounce from rich to lean, like it's getting a bad signal for something that is making it go one way or the other, then it corrects itself and goes the other way. It does not level out lean or rich.
What else can I look at besides fuel trims? My diagnostic tools are limited to an OBD2 scanner an the Torque app. So it is one way communication and I can only see temps, fuels trims and O2 voltages. I am willing to buy a more advanced scan tool if I someone can help me with ideas on what to look at.
Ruled out: IAT, IAC, MAF, EGR, vacuum leaks, fuel pump, temp sensors, TPS

 

You say the MAF sensor is ruled out, was it an OE unit or an aftermarket brand? Did you clean it with MAF cleaner? Any new codes since the beginning of your thread? I had lean and rich codes and fuel trims jumping around for my 2000 Expo 5.4, replaced the MAF sensor (after research) with a non OE part and the live data still showed the fuel trims jumping around. I bought the OE unit the next month, I believe it was Hitachi like the IAC, and my problems were solved. The OE Hitachi MAF part literally fixed the fuel trims and lean/rich condition and the Expo ran like new. Every now and then, people get bad parts from the store, it happens. Give it a good spray cleaning with engine off, then spray it with your engine running and watch the fuel trims dance around. Is the fuel filter is good? Heck, if my daughter was still at UC Merced, I would stop by on the way up to help you figure this out. I would hope that it is something fairly easy to fix, I'm still thinking IAC or MAF sensor.

 

I cleaned the IAC had had some improvement. So I went ahead and replaced it. The MAFwas replaced about 2 years ago with a motorcraft. It still tests fine. I ran it again in the morning when cold and watched the O2 closer. They were pegged at .9v so it is rich.