Never mind. I think I'd get a DTC P0455 so this scenario below is incorrect.
Since I'm still having intermittent Lean codes also, I had a thought (scary ).
If there was a leak in the fuel tank purge line from the firewall mounted solenoid to the tank and the solenoid opened, wouldn't that cause a lean condition?
I ask cause some of those soft lines along the way back to the tank look pretty bad.

I even took Carb/Throttle Body cleaner and sprayed it on every gasket, seal and hose while it was running to check for a higher idle therefore a leak and nothing.

 

Finding air leaks:
The problem often run into when trying to find an air leaks with sprays is the Ox sensors detect it and cause a correction to be made at the IAC so you so don't see much of a change if the system still has wide range correction ability.
This is the way the system is supposed to work to keep idle within +/- 50 rpm.
The better way to see the effects of the spray is to use a Scanner to watch the short term fuel trims for a reaction to the spray if they detect it.
This reaction IS the idle correction that is applied through the PCM to the IAC.
The correct idle speed is determined by comparing the idle speed detected by the front Crank sensor to a fixed program table so the difference is applied to the IAC until the Crank sensor and the table agree within +/- 50 rpm.
Very clever!
This way you can tell where and when the reaction occurs.
In other words the system out smarts you just waiting to hear a idle speed change you don't see and hear happening..
Good luck.

 

I'll be darned.
Thanks buddy
YOU - are a wealth of knowledge!

 

Still getting p0171/p0174 codes. I haven't had much time to work on it, but I'm pretty confident that I have ruled out a vacuum leak (smoke tests/propane, etc..). I did a fuel system pressure check with an Actron gage on the fuel rail. The pressure was 28 psi at idle and 26 psi at 2500 rpm. I have read that the spec is 32 psi. The fuel filter is new, the fuel pressure regulator is new. The fuel pump has about 38,000 miles on it. Does the pressure seem low enough to cause the lean codes? Thanks

 

At least for now, codes have not returned since I replaced the fuel pump. I made a rig with a cowl mounted gage that let me watch the fuel pressure while driving. The pressure dropped under hard acceleration. The pump was a Carter with only 32k miles. I installed a pump fom Autozone for $94 with a lifetime warranty. My pressure is now 32 psi at idle and actually goes up a little while accelerting. Thank you for all the help.

 

Stoked you solved your issue (thus far) I'll have to keep this post in mind if my lean codes come back. I did find a vacuum leak coming off one of the DPFE hoses so that pretty much says it for me. But who knows.

 

Here are some pics of my temporary remote pressure gage. I needed some practice posting pics here since I forgot how. The fuel rail thread is 1/16" NPT.

 

Pounder, I have not logged on in a while, so I just now read your entire thread. I kept expecting someone to tell you to check fuel pressure, but it didn't happen until post #13. I was surprised.

It's too late to help you now, but I will post this in the event someone comes looking for an answer to the same, somewhat common problem.

When you get a lean burn code, the first thIng to do after drawing the codes is connect a mechanical fuel pressure gauge. If the pressure is below spec, which is 35 to 45 on these, disconnect the vac line to the regulator and the pressure should rise significantly. If it stays the same, and there is vac at the line, pinch off the return line while watching the gauge. If the pressure doesn't rise the line or filter is plugged or more likely the fuel pump is bad. If instead pinching the return line makes the pressure rise, the regulator is probably at fault.

Sorry I wasn't here in time to help you pounder, but maybe this post will help someone in the future.

Oddly enough, I came here tonight to get a recommendation for a quality fuel pump. My wife took my Dad's 35,000 mile 98 F150 when he passed away a few years ago and it needs a pump. I don't want to pull the bed more than once, so I want the best one I can find. I don't want a lifetime guarantee unless they will put in a pump if it fails, I want a quality pump.