I have these codes up for system too lean, bank 1 and 2, and 430: catalytic system below standard. My Explorer is rough idleing in the morning, or even stalling out. Once I accelerate or after a few moments, the rough idle is gone and the car rides great.
I suspect water is condensing/mixing in the gas line. I used Carb Cleaner to check all over the top of the engine for vacuum leaks and found NONE!
I've treated the fuel tank with sea foam to try and fix the water problem in the gas, but it isn't a solution.
Intake manifold gaskets are one common issue for a lean condition contributing to a rough idle. I'd also suggest you consider the Differential Pressure Feedback EGR (DPFE) sensor as another common issue on the Explorer that could cause symptoms and codes such as you describe. Whatever the issue, you want to remedy it as soon as possible to hopefully avoid more costly damage to your catalytic converters.
It could be either the intake manifold gasket, the intake air tubing between the MAF and the throttle body, or the DPFE. I'd start by checking for a vacuum leak and if you don't find one, start with the DPFE.
I also have the same P0171 code. Was driving to a friends house an hour and a half away this past weekend and the truck drove perfectly fine until I got there. Weirdest thing for it to happen so sudden. Since then it's been idling rough, hesitates when I accelerate, some pinging and generally running poor. I replaced the fuel filter and air filter and it ran a bit better but still far from perfect. I have a 98 Explorer with 4.0L v6. Any ideas?
Pinging and rough idle, i'm willing to bet you got a bug on your MAF sensor. remove it and clean it off.
If there's a bug on the MAF you also need to figure out how it got past the air filter and remedy that. WJBentley, you wouldn't happen to be running an aftermarket reusable air filter, would you? You also need to make sure the intake air tubing didn't fall off and that some vacuum line didn't crack or come off. Since you only have a code for one bank lean I'm suspecting more of a vacuum line or intake manifold gasket. An issue with the MAF or intake air tubing would likely trigger a code for lean on both banks.
Turns out the plug in the number 6 cylinder was bad. It was burned out so bad the firing points on the top of the plug were burned off. Hope it didn't get in the cylinder and damage the engine. I also had fuel injection treatment done. Runs like a champ! Thanks to everyone who posted a reply. You all did truly help me.