I have looked this up and although there are several threads that have similar issues the issue i have seems to be a little different in some respects.

I started out with my 2000 F150 with a 5.4 V8 running rough at idle. It would idle way down slow and then rev up a little over and over. On a couple of occasions it would even die when in drive or reverse. I did finally get a Check Engine light so i put it on my diagnostic program to see what was up. Here is what I got:
P1151 Lack of HO2S21 Indicates Lean
P0171 System Too Lean Bank 1
p0174 System Too Lean Bank 2

After doing some reading up I checked all my vacuum hoses and cleaned my mass air flow sensor. I then got the same codes again after a few minutes of running. So I went to the next thing that was recommended, the upstream bank 2 O2 sensor. After changing it the truck ran fine for a couple of days, no issues. Then all of the sudden it idled a little funny again and I got a Check Engine Light again. This time:
P0171 Bank 1 Lean
P0174 Bank 2 Lean
P0300 Random/Multiple Misfire

I reset the light to see if I would get the same again later. Before the light came on again I filled my truck up with gas and it seemed to be running pretty good again. Then a day or so later it set the light again. This time:
P0171 Bank 1 Lean
P0174 Bank 2 Lean
P0136 O2 Circuit Malfunction Bank 1 Sensor 2
P0156 O2 Circuit Malfunction Bank 2 Sensor 2
P1131 Lack of Switches HO2S11 Lean
P1151 Lack of Switches HO2S21 Lean

I went ahead and drove for a few days as it had gotten really cold here and I didn't feel like messing around in my shop since it isn't heated. A couple days ago I needed gas so i filled up again. Suddenly the problem was gone again. Truck ran fine idled fine no missing or odd idling at all. That lasted a day or two before it started acting a little weird again. At that point i was down about 1/8 of a tank from full. I have read that there can be issues with the fuel pump.. I am kind of wondering if that may be it now. But I haven't had to deal with this sort of issue before so I am unsure what to check next. The truck always runs fine off idle, it only seems to have the issue when it is idling. I had reset the codes the last time and i have the light on again now. I haven't checked it yet but I am sure it is going be some combination of what i have had in the past.

I have read that the IAC valve can be an issue as well. I had a problem with mine sticking a couple years ago and when it would do it you could just tap it with a wrench and it would idle up. But it never died like it does now and it would also idle a lot slower than it does. Back then I cleaned the valve and had no more issues with it. The truck has always had times when it would act weird at idle usually after slowing down after being at highway speed. The current issue happens at all temps cold or hot.

Any Help is greatly appreciated!

 

Also FYI for anyone that can shed some light on this...

I have checked the elbow on the back of the intake. I also checked the fuel pressure, it seems to be holding steady at 30psi, although like normal the truck has not missed a beat today while I have been checking things.... . I was hoping to catch it running rough and see if the pressure had changed. I did go ahead and change the fuel filter since it had been a while. I just let the truck run for about a half hour and it is running as smooth as it ever has.

But never the less, I would like some ideas so I know what to look at next if it acts up again.

 

probably needs intake manifold gaskets. it wont fix itself.

 

The 171/174 codes tells it all.
There is a vacuum leak that has shifted the fuel tables for both banks because it's common to both.
The shifted tables sets the codes and causes poor hot idle and stalling.
The rest of the codes are sympathy codes and will clear when the leak is fixed.
Good luck.

 

Would a vacuum leak show up doing a vacuum test with a gauge. I know it always did on older vehicles. At least if it was very bad.

 

Oh and would a intake gasket leak show up by spraying some starter fluid around the gasket.

 

Vac leak on a gauge, no. If it was that bad it would not be hard to find.
Your dealing with sensors whose sensitivity is many orders of magnitude more sensitive hence the codes.
Using a combustible to find a leak requires the use of a Scanner to look for reactions on the short term fuel trim readings when the Ox sensors detect the changes in combustion gas sampled.
Do not expect idle rpm to change as an indicator. It's not a reliable indicator.
Good luck.

 

As strange as this sounds, unless you have access to a smoke machine, you can blow lots of smoke from a cigar down the big vacuum booster hose and in many cases you can see the leak.
Best of luck and Merry Christmas.

 

I just bought a 2003 F-150 5.4 and I am having the same problem. I am getting Code P1131, although I try and do most of my work myself on my vehicles and not spend money that I don't have, I am not a mechanic by any means. I was able to clean my MAF sensor and changed the air filter but no changes. I am idling rough and lately I have stalled at red lights a few times. Anything above idle it runs just fine. I have had this truck less than a month. I could use some help also on this.

 

I will try again to explain this.
The Ox sensors detect too much air in the exhaust gas.
This signals the computer to shift the fuel tables RICH for both banks.
This sets the codes you have plus other related codes.
The RICH conditions causes stalling from too much fuel because the tables are shifted Rich.
The Ox sensors are not the cause of the Rich condition but only detects the excess air in the intake tract at which the system tries to correct by shifting the fuel tables.
This brings on the stalling and rough idle condition.
If the system was not engineered to work this way, provide the codes, you would never find the cause without some far fetched luck.
Find and fix the vacuum leak.
Good luck.

 

I recently replaced my fuel pump on my 99 5.4. It gave similar symptoms as to what you stated. Mine would run okay one day and give a fit the next. It would start and run then idle like crud or completely stall out and die and would be a pain to get started again. Threw codes just the same. It eventually progressed and wouldn't keep rpms while I was driving and would bring me to the side of the road. If I'd get out and smack the tank and start it up again it would be okay for a little while. Over time it just got worse and worse to where I couldn't make it anywhere. I went ahead and replaced the pump and strainer (to get the extra warranty from advance auto). After one month I have not had any further issues. I hope I don't jinx myself.

If it does it seems to become more persistant that's where I would start. I purchased the pump and strainer alone for about $100. It's not pleasant to drop the tank, but it is how I did mine and it worked.

Best of luck hope you can get it take care of!