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Ford Truck Club Forum > FORD F-100 | F-150 SERIES > 1973-1991 Ford F150



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  #1  
Old October 8th, 2012, 09:56 PM
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Default 1991 f150 5.0 efi

What causes engine to idle too fast 1700 RPMs?
  #2  
Old October 8th, 2012, 10:05 PM
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At all times? Just at start up? In gear? In park? A few more specifics might help us narrow down the cause. Don't want to throw a hundred different things at you and then have you hope one of them will eventually work.



1994 F150 XLT ExCab SB 306, 4R70w, 8.8 3.55 open, MSD StreetFire coil, Taylor Siro Pro wires, MSD cap and rotor, 1.72 Roller Rockers, 2º cam advance w/ Cloyes Street True Roller timing set, Flat top Hyperutectic pistons, Flowtech Long Tube headers, Xpipe, High flow Magnaflow converters, Spintech XL Sportsman DIDO muffler.

  #3  
Old October 8th, 2012, 10:13 PM
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It idles high at all times. Have checked and cleaned IAC.
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Old October 8th, 2012, 10:26 PM
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I would take a look at the Throttle Position sensor. Here is a link that describes it better than i can.
http://oldfuelinjection.com/?p=30



1994 F150 XLT ExCab SB 306, 4R70w, 8.8 3.55 open, MSD StreetFire coil, Taylor Siro Pro wires, MSD cap and rotor, 1.72 Roller Rockers, 2º cam advance w/ Cloyes Street True Roller timing set, Flat top Hyperutectic pistons, Flowtech Long Tube headers, Xpipe, High flow Magnaflow converters, Spintech XL Sportsman DIDO muffler.

  #5  
Old October 9th, 2012, 09:41 AM
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How did you check the IAC? What happens if you unplug the IAC while the truck is running? Have you checked for vacuum leaks? If so, how did you check?

After all that, I'd check the TPS voltage as well, should be at .97v.


89 F-150 5.0l AOD 2x4, 3.55 LS(+4), Converted to HO Roller, 3g Alt, GT40Ps, Y-pipe, Rerouted PCV, Dual Taurus E-fans, Explorer Injectors, Remote ICM, DIY Cold air, Rubber Vacuum System, Tranny cooler, Remote Tranny filter, Saginaw P\S swap, F350 Brakes, more.


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Old October 9th, 2012, 10:38 PM
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I checked the iac for resistance with a voltmeter and it checked good according to haynes manual. The truck still runs at high idle when the iac is unplugged. I just checked for vacuum leaks by hand, have not sprayed any flammable material on there. We are in the process of trying to do an sti but are learning as we go. The check engine light is not on.
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Old October 9th, 2012, 10:46 PM
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Run the codes anyway, It's simple to do with your truck being obdI. I'm not sure if there is a thread for it on here yet or not? I could make one tomorrow I guess.
I also have yet to see a good way for checking the IAC besides unplugging it and seeing what the truck does. IIRC mine runs at a high idle for a little then dies.


1990 F150XLTLariat. 300I6. ZF. BDS. 36x16.5x15FC. SAS under construction.

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Old October 9th, 2012, 10:59 PM
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I did a thread for OBD-1, lemme grab it.
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Old October 9th, 2012, 11:02 PM
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http://www.fordtruckclub.net/forum/s...ead.php?t=6720
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Old October 9th, 2012, 11:07 PM
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I would like to add to that thread soon if that's okay with you blue, with how I do the codes and a video of actually pulling codes.


1990 F150XLTLariat. 300I6. ZF. BDS. 36x16.5x15FC. SAS under construction.

How to: FTC Gallery.

How to: Brick steering column.
How to: Wiper motor removal.
Shop Class 101.
Door Tag Codes.


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