Got iac at junkyard. Cleaned it up, installed..hooted at first but the noise subsided. Short test drive and everything was good.
Today, longer drive about 23mi still good. parked for about 30 min, then shortly after take off CEL appeared. After that, i noticed a bounce in rpm while coasting for a min then it was normal.. continue driving - then few miles later did the rpm drop while accelerating like it wanted to stall but as i kept on the gas, it pushed through the jerking and went back to normal. Kinda did that maybe twice more but not as bad by the time i got back home.

once home, pulled the codes:
P1443
And pending P0102

i did have the p1443 pop up once before during all of this but had figured something related to all the stalling at random times and fumes not purging where/when they should..
fyi, i did replace the vac line between throttle body and charcoal canister, purge flow solenoid and thermistor all as one assembly maybe 6-7 yrs ago (oem)

Other than being brittle from age alone, my wires and harnesses all appear in tact and not compromised

I do believe the delphi iac was giving me some of the problems, but now I'm still wondering if the PCM is acting funny - be it from corrosion or programming..?

I also wonder about some slight transmission issues (tcc or downshift solenoid) but it's a whole story that i would have to start a new post with the details on that. Want to figure this apparent air flow issue out first and see if i still have the other symptoms I've experienced.

 

P0102 Mass or Volume Air Flow Circuit Low Input
P1443 Evaporative Emission System Control Valve (low/no flow)

Both are "air" codes

Computer knows its running a 4 Liter engine, so it already knows EXACTLY how much air is coming in at any RPM, its just math
What it doesn't know is how much the air that's coming in weighs
Air:fuel ratio for gasoline is 14.7:1..............and its a WEIGHT RATIO
14.7 pounds of air to 1 pound of gasoline
14.7 grams of air to 1 gram of gasoline

P0102 means MAF sensor shows air weight that is too light for engine RPMs, so you are either driving at 10,000ft above sea level or there is another issue, lol
MAF sensor is there to WEIGH the incoming air, that's the "Mass" part of mass air flow(MAF) sensor

Air weight changes by temp and altitude above sea level, "hot air rises" because its lighter than cold air, its how hot air balloons fly
And air is "thinner"/lighter up in the mountains

Clean MAF sensor, check connector for corrosion


EVAP system sucks air out of the gas tank, well gas tank is sealed so it causes a negative pressure in the gas tank so gas fumes won't escape and pollute the air
Get a hose and a damp cloth
Take gas cap off and put hose in the opening
Wrap damp towel around hose to seal the opening
Blow into the hose
Listen for escaping air, best to have a helper for this
Listen by filler hose, most common place for a leak
Listen in engine bay, hose from gas tank to charcoal canister

DO NOT use an air compressor for this test, you will blow off hoses
Human lungs can generate maybe 2psi, so can't blow off anything, lol

 

Didn't know if this is also worth mentioning, when i previously had the p1443 code (only once) i did also have p0174 at the same time if I'm remembering correctly.

I did change one of the O2 sensors last year prior to the random stalling. I can't recall which bank (i was a bit confused to finding them all, only 3 total on this 4.0?) I should have probably changed them all for age alone..

 

I did also replace the fuel filler neck about 5-6 yrs back, knowing that the only replacement i could find was not going to last as long as oem. I have not heard the pressure releasing noise from gas cap for a long time (years) but never really had any starting issues long as i let the pump prime before cranking.

Could a leaking filler neck also aid to the stalling..??

 

Might be a silly question-
how does elevation affect the motor?

Truck was bought and driven in North Georgia area 1997 between 1,200-1,500'

Moved to metro Atlanta area in 2014 around 1,000'

Now in Jacksonville florida as of 2020 <25'

I've made many trips back and forth from all these areas and only once in a while had a lean code (when i wasn't fixing other problems) during my travels.

*edit* i suppose this question was irrelevant. I'm guessing even at a 1,500' gradual range of altitude, it should not affect the motor too much

 

Had to get a hose and a helper, going to do that blow test later today.
*UPDATE *EDIT* test was performed but i could not tell that any air was escaping, and the pressure def built up when blowing into the hose.*


But in the meantime, i was looking at the vac lines again, and took the charcoal canister off. The small hole is the in flow? I blew into that and it was very difficult and not much air came through the large hole. Shouldn't this be free flowing? I wanted to stick my pick in the hole thinking some charcoal might be clogging it but i did not know if i would be piercing anything inside by doing that? - i assume it's okay but could not find a diagram to be sure.

I also am guessing the canister needs to be connected back before i blow in from the tank as you suggested?

 

Oh goodness! While looking at live data on the scanner today, i noticed my IAT reading was super high indicating around 130 degrees when the truck was barely to temp.. and after sitting off over an hour now it still reads over 120.. it's been around 85 outside during all of this.
I'd say this sensor is bad.

When i observed that reading before, i may not have been paying close enough attention. I remember it being closer to the actual temperature at cold and hot and haven't really focused on those numbers since then.
could anything (power/ground) cause a false reading other than the sensor itself being bad?

*UPDATE*
Took out the iat sensor (first time ever removing it) and it was dirty on the incoming air flow side, and basically clean on the other side. Normally this sensor should be within a 10 degree or so difference from outside temp from all I've read, but can have heat soak and read a bit off at times, yes?
3hrs+ after truck was turned off (only having ran about 10 min in park- only crank of the whole day at that) as well as after bringing the sensor inside the house to clean it (used the maf spray), i checked the reading again after reinstalled, still reading 99 degrees on the scanner. Just want to verify that that still seems inaccurate as i think it should be much closer to 80degrees or less at this point..?

I don't know that anyone is still reading this post where I've started asking all the silly questions..but as much as i try to "keep it simple, stupid!" i also like to way over think..esp while I'm still learning about things. . .

 

Fixed.

I want to share my experience because I'm sure there are many lessons to be learned here..

Turns out i created a DIFFERENT stalling issue in January at the same time as fixing the initial stalling issue that began in October last year. Then it took 6 months for that *error* to finally rear it's head..

Short version: came down to a loose connector. D'OH!

The very first time my truck ever died suddenly/randomly was last year. I hit the brakes a little hard while making a right turn, that was also over a big bump, so it bounced a bit hard too. It took me a few seconds to even realize that my truck had stalled. Scratched my head, started it right back up, went on my way.

Took a few weeks maybe before it stalled the second time. Was coming to a red light that i stopped hard at then lost power. That became more frequent and stayed consistent with me making a harder stop -vs softly braking or coasting didn't seem to do anything strange. Twice it would not turn over after power loss, seemed as if it was starved for gas. Had it towed, then it started just fine.

By January, i had already looked over things and spoke to lots of people and was limited on things i could check for that i know needed to be checked because i didn't have the tools/ equipment. Frustrated, i actually took it to the stealership for a diag that i was already expecting to not fix my issue. There's a whole story in that as well, but i won't burden you with that lol. They came back with "wiggle tested and maf sensor was erratic" and said "that may or MAY NOT fix your issue."

Knowing i could change that myself, if that's actually why i was stalling, i decided not to pay them the 400$ they quoted me for that. I asked if i were to do the job myself and if it didn't fix the problem, if they would charge for another diag. They offered a small discount but i was a bit discouraged at this point. The only part i had replaced while looking for the problem so far was the IAC Valve in December- which i think was dying just by coincidence now that this is all over..

I try not to just throw parts at the truck- but if i can do that way cheaper than going to a shop, then yes, I'm guilty of loading that cannon lol. Well, i opted to get a new maf sensor just to see what happens, as i had run out of ideas at that point.

Changed it out, still had a stall when coming to a stop.. don't recall if it was as hard a stop or a bit softer than the usual..but seemed like the same symptoms more or less. Spent next few days with another mechanic, and eventually we started messing with the inertia switch (which i did inspect before, without jiggling it around tho) and the stall was recreated. Opened up the switch itself and saw the ball that makes contact was slightly coated with corrosion. That very first stall, the bounce likely jostled it and now the ball had a weak contact..decided to jumper the wire to bypass the switch and see if that worked. It did not stall at a hard stop anymore! *which i mentioned in the original post* so i rewired instead of getting a new switch.

Couple weeks go by and i noticed a slight change in things- i seemed to almost stall but then not and then immediately stall right after while braking, more often while turning. Started stalling at idle after a slight stutter. Started stuttering and losing power while driving.. I thought my original stalling problem was back and just getting worse and wondering what was about to break very soon that i was over looking?? Did i mess something up by omitting that switch with my rewire? Not all stalls are created equal haha.

The connector pigtail for the maf sensor was a bit tricky for me to get attached through the housing.. and i did the best i could back in January being very careful while installing. The replacement i got did not have the bump for the locking tab to clip to, so i never got that satisfying click to ensure the connector is fully attached. It took 6 months to wiggle loose enough to finally throw a code, but was giving me so many random and intermittent issues without any codes when it wasn't making good contact. I regret that this was in fact THE ONLY connector i did not double or even triple check after going through each part /repair i had done over the last 6 months. I honestly forgot about the connector inside the housing being something i needed to check again- until i planned to put my old maf sensor back in thinking the new one might be defective. When i went to switch them out, that's when i immediately realized my mistake!

Original maf sensor is back in (it was perfect to begin with) and connector is locked in place. No more stalling.

At least because of my own blunder, i now possess better knowledge and some new tools to use to my advantage.

 

Just an update-
Still throwing the p1443 code for my evap.. and there is a hard (slow) start when warm now, as if the vapor fumes are trapped - likely related to the code I'm getting.

I was trying to improve other things when i started this thread about the stalling..but even tho I've likely created the evap low flow from all the parts i messed with, i was still looking for input without making a new post.

I am looking for vacuum leaks based on ron's recommendation in fuel vapor lines, and the egr i replaced also has me questioning that area now.

if anyone has more suggestions, I'd love to hear them. I really doubt the purge solenoid itself is bad, which is what most of the locals would recommend changing without offering any real assistance..
despite my earlier blunder with the loose connector, i promise that was the only one!

 

Get a hose and wet/damp rag/towel, garden hose/heater hose size
Remove gas cap and put hose into filler neck, wrap damp rag around hose to seal it
Blow into the hose
Gas tanks are sealed so you should be able to build up some pressure, if not you WILL hear where air is escaping
You may need a helper blowing into hose so you can listen in engine bay

DO NOT use an air compressor for this test
Human lungs can generate maybe 2psi of pressure so not enough to blow off any EVAP hose fittings
Air compressor WILL blow off EVAP fittings, for sure

 

I tried your recommended test, and was not able to detect any obvious air escape or pressure loss when blowing in the tube. doesn't mean I'm ruling that out though. Keep looking at all my vac lines in the evap line and they seem okay..

related to the slower warm start i have started having-
It seems my fuel pump might be failing again. I had originally replaced the factory pump in 2020 with a delphi (I'm starting to hate this brand!). It worked just fine, but when i was having my stalling issues, i warranteed it out, basically just for fun to rule it out as the culprit when i got stranded twice.
the replacement had a malfunctioning sending unit, the dash gauge would read empty after a fill-up..so another warranty exchange. Now with this current pump, i keep hearing a faint whine (not all the time but i may just not always notice) that usually diminishes after warm up- but i honestly can't tell if it is truly coming from the fuel pump or my transmission because I've heard similar noises before the current pump was installed..

But today after a drive and park, when i started the truck, kind of sputtered a bit with rpms extremely low and bogged out after a few seconds essentially stalling- and that's when i heard the fuel pump gurgling a whole lot.. turned KOEO twice to prime the pump just in case and everything good when i started the truck again. Got home and parked, then immediately cranked again to see what happens and everything is fine- no gurgling. Let it sit an hour and then with KOEO i could hear the pump gurgling again as it primed..it started fine and only briefly bogged for half a second and was good.
I pulled the vac line off the fuel pressure regulator again to be sure that it was still dry.

It's odd to me that i don't need to prime it on cold crank - but i don't fully understand open/ closed loop and when pcm is telling things what to do etc.. but maybe that's the "delay" that is hard for me to describe at cold crank- which i only started really noticing and paying more attention to since after the last pump install and don't recall if it happened before that.

also, now my IAC is hooting (one from junkyard, pretty sure is oem). I'm hesitant to put the delphi back on as it isn't really the proper one to use from what I've been told. I have one more from the junkyard that came off a Mazda (doesn't look like a motorcraft, not sure if it's a hitachi tho) that i have not cleaned up and tested yet, but also hesitant to do that so as not to create even more issues. . .