That's your IAT.

 

Intake Air Temperature (IAT) = Air Charge Temperature (ACT)

 

well what ever it is called, thats what i cleaned to get an improvement out of the truck. I called it air charge sensor because thats what autozone called it...i had never heard of it before.

 

Yea, means the same thing, Ford lists it as an IAT. If the IAT malfunctions (which is rare, unless you fubar cleaning it), you'll get a CEL. That was the last problem I worked on with the 98 truck (5.4L), I had a CEL and a DTC pointing to the IAT. I happened to have 3 new IAT's on the shelf. BTW- the engine would idle fine, then get goofy, then fine again while this problem existed. I swapped the sensor, reset the KAM and got the CEL again with the same DTC. So the problem had to be harness oriented. Sure enough, the VREF wire was showing no voltage, - the wire separated inside the insulation before the connector. The other problem you can have by that sensor is with the grommet. The grommet can dry out and crack with age. That can lead to PO171/174 as far as DTC's.

 

okay well i replaced that sensor...only 15 dollars so not a big expense...havent driven it much, i wanna say i have more power but idk if thats me just wanting to have more power. lol
had the check engine light come back on...took nearly 200 miles for it to come back on. same code...misfire 4.

because it took so long to come back on, is it getting better? lol it used to come on within 50 miles.

one thing that i have not done is a compression test...i have heard of these before, though i have never done one or even read about one...i guess i should do that.
im kind of scared to know whats wrong if the compression test does show something bad..

 

you also need to clean the MAF...

 

done that twice already ^^

 

well i got a diode tester and tested my injector harness...that works fine. then i got a hold of a compression test guage. thats when the real fun came out.
0 PSI in cylinder 4...well crap. dripped some oil in the spark plug hole to check for bad rings...still no pressure. so this leads me to believe stuck valve or damaged valve.
(still could possibly be a hole in the piston...unlikely and would probably show a little pressure unless its a big hole...and in that case im sure i would have other issues)
so i did a little reading...read about this oil and gas additive that some people say works wonders...Marvel Mystery Oil. I added the appropriate ammount to my gas, then put the rest in my oil (yes checked to make sure it didnt over fill...i had room for extra fluid in there as it is about time for an oil change anyways.)
now as for the results...i dont want to be too optimistic but it feels to be improving the more i drive. had an hour drive last night...first was misfiring as always...then the misfire became intermittent. I havent driven it much today but the misfire seems to be less...cant really tell if it is fixing a stuck valve...or is it just making it run better period because of the additive..
either way i think I am going to pull my valve covers off and do a little looking...see if i have a broken spring or stuck rod or something.
Yall have any opinions?

and to anyone who ever has a misfire that isnt solved with a plug or wire or vaccum leak...do a compression test. you can rent it from autozone and get your money back...saves a lot of time. I never did it because i had not thought of it and then didnt know what it entailed to do so i wasnt confident. but very easy to do and well worth the time.

i think im finally on the right road to solving my ongoing truck problem...now most everything that i replaced in trying to figure this out would have needed to be replaced anyways...i went from like 8 codes or something down to 1 last code.

plus i learned alot. thanks everyone on here cause this is where the majority of knowledge has been learned from.