Idle issue nightmare
Fleet Owner
Joined: Oct 2005
Posts: 20,786
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From: Kentucky
1987 through 1995 for the F150/F250LD/Bronco. If the F250HD/F350 could be ordered with a 4.9L engine then that would extend to 1997 for them as long as they are EEC-IV. I am not aware the EEC-V trucks with the 4.9L engine use this methodology.
Freshman User
Joined: Sep 2010
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Likes: 1
I'm not sure if he replied to this, but Will is my Dad. I unplugged this when it was idling high and this brought the idle down.
Freshman User
Joined: Sep 2010
Posts: 35
Likes: 1
Also, just to add a little bit more information to this thread. The high idle is sporadic. When I witnessed the truck idling high a few weeks ago it idled for at least half an hour at a seemingly normal idle, then out of the blue it went up to about 3k and stayed there. This is when I unplugged the IAC and the idle went down.
I sprayed all over the engine bay with carb cleaner and I would not get the idle to go up...so I don't think there is a vacuum leak, but I am not 100% sure. He has my Actron CP9145 scanner, so I would think it can scan his truck. I really thought this was pointing towards a cpu problem, but now he has changed that and the problem seems to still be there.
The truck also has issues with stalling out and not being able to restart once it has been driven for a while, but this is also sporadic and I don't know if the two problems are related, but I just thought I would throw out some more information.
I have a vacuum gauge at home, what vacuum reading should this truck show without vacuum leaks?
I sprayed all over the engine bay with carb cleaner and I would not get the idle to go up...so I don't think there is a vacuum leak, but I am not 100% sure. He has my Actron CP9145 scanner, so I would think it can scan his truck. I really thought this was pointing towards a cpu problem, but now he has changed that and the problem seems to still be there.
The truck also has issues with stalling out and not being able to restart once it has been driven for a while, but this is also sporadic and I don't know if the two problems are related, but I just thought I would throw out some more information.
I have a vacuum gauge at home, what vacuum reading should this truck show without vacuum leaks?
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
Computer controls the timing when the SpOut connector is in, it uses different strategies for different driving conditions.
What is your timing with SpOut out? With SpOut in?
Last edited by vjsimone; Dec 10, 2018 at 09:10 AM. Reason: Deleting questionable text...
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
You can tape off the Throttle Body intake and blow cigar smoke in the power brake vacuum hose.
Also, you can cap off all the ports on the vacuum tree, run new temporary vacuum lines to the MAP & FPR, this will eliminate all the old vacuum lines.
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
17-22 in Hg @ 650-700 rpm
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Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
There is also a good chance the computer itself is going bad. Open it up and inspect for signs of burned components and/or leaking capacitor(s).
The lack of ability to pull codes is another sign the computer is suspect. Not sure if you have tried with the clutch depressed as outlined earlier.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
Also, just to add a little bit more information to this thread. The high idle is sporadic. When I witnessed the truck idling high a few weeks ago it idled for at least half an hour at a seemingly normal idle, then out of the blue it went up to about 3k and stayed there. This is when I unplugged the IAC and the idle went down.
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Cross-Country
Joined: Sep 2018
Posts: 95
Likes: 0
Ok heres the latest -vltage to the IAC IS GOOD 14.50 --UNPLUGED THE IAC -idle went back to a more reasonable range . from 3k to 1 k . Got the distributer where it will rotate . disconnected the spout --went counter clockwise (retarding direction I think) a little . No timiming light . plugged spout back in .. Idles good 800-900rpms . Plugged the IAC back in --idle increased to 1500. --unplugged it again --drove it 10 miles or so -- - also when I unplug the MAP SENSOR ,idle will increase a little .
Can I just leave the IAC UNPLUGGED ??
Can I just leave the IAC UNPLUGGED ??
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
If you will run your diagnostic codes that should help find your problem. Actually when you unplug the IAC it should die or almost die. The idle you get when unplugging it is the lowest it will go in its condition. With the spout out, your computer no longer controls idle as you have taken it out of service for idle. You are not ok leaving the IAC unplugged, something is wrong. In reading your post did you try to set timing with the IAC unplugged? If so you didn't do it right.
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Cross-Country
Joined: Sep 2018
Posts: 95
Likes: 0
If you will run your diagnostic codes that should help find your problem. Actually when you unplug the IAC it should die or almost die. The idle you get when unplugging it is the lowest it will go in its condition. With the spout out, your computer no longer controls idle as you have taken it out of service for idle. You are not ok leaving the IAC unplugged, something is wrong. In reading your post did you try to set timing with the IAC unplugged? If so you didn't do it right.