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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

Erratic idle

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Old Feb 11, 2023 | 08:27 AM
  #1  
octaneforce's Avatar
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From: long island
Erratic idle

Hey folks i used to be on here alot. About 5 years ago i put my truck into storage because it had an issue that i gave up on dealing with. Well it sat in a garage for all that time and ive decided recently to put it back on the road. 1992 f150 inline 6. Truck is in my signature

it runs poorly when hot. It has a weird random miss and generally lower on power than it should be. It also will suddenly idle very high. I did EVERYTHING on this truck before i put it away. Im starting over today with a regular tune up. (Cap rotor wires plugs coil bla bla bla). I am weary of some non motorcraft parts in there which is what I’ll be replacing everything with. Only motorcraft here on out.

my question is, do you think this could be a bad computer? Its the only thing i havent messed with. They seem fairly available. Not sure if theres any sort of flashing process to replace it. Im just at such a loss with this thing but i miss driving it.




 
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Old Feb 11, 2023 | 08:53 AM
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Have you cleaned or replaced the IAC valve?
 
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Old Feb 11, 2023 | 09:07 AM
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Originally Posted by jas88
Have you cleaned or replaced the IAC valve?
yep several times. Currently its a motocraft replacement. However its from when i put the truck away so its about 5 years old. Was debating throwing another one at it to try and get a baseline.
 
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Old Feb 11, 2023 | 12:20 PM
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There are 3 wires that connect to the coil plug, but only 2 seem to go anywhere. One of the green wires is just sitting there. Where is this supposed to go? If that wire has a purpose this could be the root of my problems, or atleast most of them
 
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Old Feb 13, 2023 | 01:33 PM
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This diagram only shows 2 wires leaving the coil plug/harness. I guess that extra wire i see doesnt do anything? Seems kind of silly. It sure looks like it used to be connected to something. Theres also alot of these replacement harnesses out there so i guess these plastic plugs break sometimes.
 
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Old Feb 14, 2023 | 08:36 AM
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I think that is supposed to go to a noise suppressor.
 
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Old Feb 14, 2023 | 01:15 PM
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Originally Posted by jas88
I think that is supposed to go to a noise suppressor.
a what? Lol. These trucks arent known for being quiet
 
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Old Feb 14, 2023 | 01:48 PM
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a what? Lol. These trucks arent known for being quiet


For the radio. It's in the schematic you posted.


What does your truck do if it is running and you unplug the IAC valve?
 
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Old Feb 14, 2023 | 02:32 PM
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From: long island
Originally Posted by jas88
For the radio. It's in the schematic you posted.

What does your truck do if it is running and you unplug the IAC valve?
oh wow right over my head! Thats hilarious.

I’ll tinker with that tonight. I appreciate the help!
 
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Old Feb 15, 2023 | 06:08 PM
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From: long island
Originally Posted by jas88
For the radio. It's in the schematic you posted.

What does your truck do if it is running and you unplug the IAC valve?
the idle gets super low if i unplug the iac.

today i also did a new thermostat, the old one seemed stuck open and the truck was never getting to operating temp. I beleive this was making it run rich. I did a new fuel filter for good measure as well. Its definitely better but something still isnt right.

i think my misfire and high idle are 2 different problems.

i deleted the smog pump years ago and theres vaccume lines ive blocked off that lead to behind the motor at the servo thing which operated the smog pump. I think that part is leaking when its actuated, and causing my idle issues.

the misfire i really dont know. Seems to occur the worst at high rpms towards the end of the powerband. Do these motors have a “rev limiter”? Mine practically hits a fuel cut at the top of the rev range
 
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Old Feb 15, 2023 | 09:12 PM
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Misfires and stumbling at high rpm could be fuel flow related
Step one is to pull codes. Even if you don't have a check engine light, you may still have codes. The procedure is here. https://www.ford-trucks.com/forums/1...aper-clip.html
Step two is to check fuel pressure. The procedure is here. https://www.ford-trucks.com/forums/1...rd-trucks.html
 
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Old Feb 24, 2023 | 04:02 PM
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From: long island
Okay sorry for the delay i finally got around to hooking my reader up to this thing. i have 3 codes

173: HEGO (HO2S) sensor fault/rich
213: SPOUT circuit open
411: cannot control rpm during koer low rpm
check

first thing i did was check the spout connector. The grey cap is definitely connected and snug. The wires seem okay. Im not sure how the spout is open. Id have to look closer at it to find a break in the wire or something further down.

411 i have no idea

173 makes sense because this truck does smell like it runs rich but that could be a result of the spout
 
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Old Feb 24, 2023 | 04:44 PM
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Were these the active codes or the memory codes?
If you removed you spout connector lately, it'll pop the spout code.

411 could be caused by someone cranking up the idle set screw. What happens if you start the engine and pull out the IAC connector? Rpm should drop to about 650 and sit there.
 
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