Above is my daughter's vehicle. Seems to run fine, but CEL was on, so I pulled the above codes.
Based on older posts, I'm wondering what steps to take. It has a K&N filter, so I'm wondering if the first steps should be:
1. Replace K&N with standard filter.
2. Replace pre-cat 02 sensor on driver's side.
3. Clear the codes and see if the P0171 and P0174 codes return or go away.
Does that sound like a plan?
When's the last time the Explorer had a tune up? If it's been awhile, you might start there since that's routine maintenance anyway. While in there, check ALL the vacuum lines and make sure you don't have some that are cracked or broken. There is a 1/2 inch diameter or so rubber elbow that is known to crack/split. It may not be obvious without flexing it. Does the vehicle idle smoothly?
I think before replacing the O2 sensor (if you don't find any bad vacuum lines, plugs, or wires) I'd replace the DPFE sensor. These are known to fail on this vintage of Explorer, Mountaineer, Ranger, Taurus, etc..
Spray some carb cleaner around the intake manifold and vacuum lines. You've got an air leak somewhere after your mass air flow sensor (MAF). If the carb cleaner gets in at the vacuum leak, the idle will change.
K&N filters may get some oil on the MAF, so it might help to spray some MAF cleaner on it. A longshot, but not unheard of.
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98 Exp 4.0 136K, CEL P0153, P0171, P0174
