I've been asking about the MAF and IAT in another thread... there are however many threads/posts about the abundant P0171 and P0174 codes (and associated problems with rough idle, fuel economy, acceleration, etc. ) Sometimes it's a bad MAF (or other sensors), or wiring(or harness), gaskets, hoses(vacuum leaks), fuel pump or other fuel parts, fuel vapor vent solenoid, or a mix of these, or maybe bad Karma...
Some rough acceleration and occasional hesitation on my 2000 5.0L V8 MM was accompanied by frequent P0171 & P0174 codes, and I decided to have a go at it (with some hearty helpers more mechanical than me) even though my Ford mechanic nephew is in jail for some time (he replaced O2 sensor, spark plugs and wires, fuel filter, and some radiator fan & air temperature sensor stuff last summer.)
I haven't gotten an elegant OBD2-scanner/Fusion, FuelPressure tester kit yet (but maybe soon) so just have the cheap code-reader codes, and reset them. (AdvancedAuto & others won't help these days due to COVID rules here.) I decided to buy a new but cheap black plastic MAF to spec, a bit set for those funky screws, and had the guys install it. They disconnected the battery and did some of the ECU reset stuff (though no revving/long idling), as I learned about Fuel Trims(long and short) and PSI and more.
Seemed OK at first; no P0171/P0174 but may have been pending(50 miles,more trips) when it THEN coded P0112(IAT.) Some indirect communication with nephew and others and reading influenced me to buy the fitting IAT sensor to spec. But couldn't find a place to put it, and (to the surprise of many disbelievers) after much effort and drama established I indeed had the model that has the IAT built-in to the MAF.
(No experts, threads, posts, or research revealed what one is effectively supposed to do when you get a P0112 or P0113 - as I have - the main remedy being "replace IAT sensor" when in fact, you really can't (other than a new MAF. Heh.)
Just for giggles, I will reveal that the part nbr on the IAT purchased from AdvancedAuto googles to "MAP sensor" even though the sensor I got looks exactly like the IAT sensor photos (that some models are supposed to separately have on the Intake Sleeve (not mine though.)) Anyway, it's still in the bag(and if we ever find where the MAP (is it actually the ECT?) is on/near the upper intake manifold, might even use it some day. After a helper cleaned off (and zipped off the leak of) some antifreeze and maybe some trans fluid, checked for rot and loose fitting and leaks, etc. I actually then carefully drove to Advanced in town to pick up the IAT, had a few stutters along the way, but when I started it to return, it lurched, shuddered, bucked, and would barely go. Fortunately Limp Mode (or whatever happens when you unplug the MAF as I did) gets me home.
Drove it with the old MAF for awhile, passably functional, while still getting continual intermittent P0171 & P0174. Meanwhile, I researched MAF and IAT and Fuel Trims, and purchased a Genuine OEM MAF to spec; was actually gray and more sturdy, and had the helper install that and do the 30 minute plus 30 battery reset disconnect stuff to clear the ECU. He then idled it 10 minutes and did this and that RPM revving. Made a lot of noise but he had a good time, as I cringed.
He then took it for a 5 minute test drive, gunning it (i think) to 65-70 3 times, and reported on the 3rd time the check engine light flashed on and off, maybe 3 times. Didn't stay on, and good it didn't keep flashing, seems to be a cylinder misfire that maybe was one-time don't sweat...
...But when I started it up an hour later, it shuddered and spit and could hardly do more than lurch. Coded with a P108 or something meaning cylinder 8 misfire. Could also see sparks, which seems to have resulted from the wires (or plugs) there just touching something on the manifold (since remedied with a separator or such.) And then it was noticed (perhaps missed earlier) that this hose from purge cannister to EVAP exhaust or whatever had flattened and sucked up, in fact, it was sort of crumbling underneath when one lifts it. And as above, a new hose now there.
I'm not sure if all the aggressive revving and driving to try and make the ECU ReLearn faster contributed to some of the above, or how ReLearning in general affects driving for a few trips and miles, maybe days or weeks, but there is not a lot of info on this out there, unless you have an advanced tuner scanner and can precisely calibrate the new MAF and watch the Historical Trim data reset and such...
...so I am hopefully (it will work it self out during the Harsh ReLearn) puttering along, as we don't have those tools nor expertise, hoping for a miracle, some magical tips, sympathy, or a good laugh. Thanks.
(P.S. Ooops, meant to mention (in case this ain't long enough, sorry) that much of these troubles seemed to start after Walmart Auto did my regular Oil Change about 4 months ago, and (for the first time) ALSO replaced the Air Filter.)