REALLY BAD high idle problem, need help!!!
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Freshman User
Joined: Nov 2002
Posts: 45
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From: Newtown PA
REALLY BAD high idle problem, need help!!!
I have a 94 f250 manual with the 5.8 motor. I've been having an intermittant problem over the summer. truck would high idle at 2000-3000 rpms. I cant drive the truck because it never drops below those rpms. Before, it would come and go, and if you would shut the truck off, it would go away. About a month ago, i shut it off at a traffic light to see if the prob would go away, and the truck wouldnt start. just crank, no run, gas smell with spark.i replaced the IAC and the truck started up high idle. did it twice then no start again. now i can only start the truck with starting fluid, then it runs high as usual. if i unplug the IAC and start it on starting fluid, the truck runs fine at 650, just cant start it. i cant figure out whats making it do this. i bought the IAC at autozone but im buying a ford one tommorow. dont know what else to check, try, replace. everything else seems good. seems like the truck is trying to compensate for a bad sensor??? or maybe a bad wire going to the IAC??? please help because this is my plow truck and im running out of time !! thanks, dan
Senior User
Joined: Apr 2003
Posts: 197
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From: Phoenix
In addition to a vacuum leak in the hoses, check for one where the intake meets the block...spray some carb cleaner around the seam and see if your RPM's go down for an instant, then slowly hone in on the problem area. This is the same exact issue my Mustang had, and for about a month I lived with the belief that it was a whole host of other problems until I tried this.
-aaron
-aaron
Elder User
Joined: Mar 2004
Posts: 537
Likes: 2
From: Alabama
Had a similar problem about (6) months ago. My vote goes to Upper Intake Manifold. Mine was idling about 2000 - 2200 RPM constantly. Front part of the gasket on the drivers side was gone. Had an engine put in and the mechanic left the brace that supports the passenger side of the manifold off. All the bouncing around worked the driver side bolts loose and it popped up. If that's what it turns out to be its not that bad. Several post on here about this. Search by high idle. Mine was "Extremely High Idle". Need a T40 torx bit,extra long, about 7-1/2" or 8" for the center bolt passenger side. Go down thru a slot in the center of the manifold from the top. Let us know what you find??
guzzler96
guzzler96
New User
Joined: Nov 2004
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bad idle
I have a 92 150 manual 5.0, that has been doing almost the same thing for the whole time i have owend the truck, 2.5 years. I have replaced the tps
the iac, the upper intake gasket, throttle body gasket twice, and so on.
I am a tech for ford, so i called the hotline and they said put a pcm in the
truck, i have no codes and nothing to go off of, so i have narowed it down to a pcm or throttle body. I recently had a 2003 mustang come in to my dealership that would do the same thing, i put an iac on it and it did nothing, than called hotline, they said put a pcm in it so i did, whell what do ya know it worked. So i am planning on replacing my pcm real soon. I hope this helps you, if it does fix it let me know. I hate shutting my truck off and restarting to.
the iac, the upper intake gasket, throttle body gasket twice, and so on.
I am a tech for ford, so i called the hotline and they said put a pcm in the
truck, i have no codes and nothing to go off of, so i have narowed it down to a pcm or throttle body. I recently had a 2003 mustang come in to my dealership that would do the same thing, i put an iac on it and it did nothing, than called hotline, they said put a pcm in it so i did, whell what do ya know it worked. So i am planning on replacing my pcm real soon. I hope this helps you, if it does fix it let me know. I hate shutting my truck off and restarting to.
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Freshman User
Joined: May 2003
Posts: 26
Likes: 0
From: Wausau, WI
I once had the same exact problem with my 1994 Ford F-150 351. I had to replace the throttle position sensor located on the bottom of the throttle body; it costs about $60. It sounds to me that you are not leaking air from a bad intake gasket, if you did your truck would not be able to idle at 650 RPM when you unplug the IAC.
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Brett Foote
Lead Driver
Joined: Feb 2003
Posts: 8,140
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From: Oak Harbor, OH
Tex is right, the TPS tells the computer where the gas pedal is. The computer in turn opens the IAC letting air in. The TPS is bad, and can be had for $35 at AutoZone. Make sure you get the gasket too, it's only a couple of bucks.