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Idle Problem

Discussion in 'Ford Trucks' started by JohnsonLawn, Feb 18, 2006.

  1. JohnsonLawn

    JohnsonLawn Member
    Messages: 78

    I have a 1988 F-250 with a 351/ auto. I am having a problem with the truck at idle. When I first start it everything seems fine, it runs strong and idles smooth, but when it warms up a little and idles down things go to he$$ quick.
    As soon as I put it in gear the check engine light comes on and the engine idles rough then stalls. This problem just started about a week ago, but is keeping me from driving the truck. Any ideas as to where to start looking for trouble would be appreciated. Thanks
     
  2. MBB

    MBB Senior Member
    Messages: 129

    You need a new Idle air control unit (basicly a very fancy choke) if your unit is fuel injected, that is what I had to repllace on a 90 302? (forget what it is metric rating) about $80-90 not hard to change out 2 bolts if i remember right.
     
  3. DeereFarmer

    DeereFarmer PlowSite Veteran
    Messages: 3,296

    Sound right. I had to do that on my '96 F150 with the 351W. Real simple change!
     
  4. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    The idle air control may need replaced,most times it does no good to clean it.
    It's attached to your intake right by where the throttle cable attach's. Your throttle position sensor could be bad also,it's mounted on the butterfly shaft of the throttle body. Make sure all the accelerator and cruise control cables are attached into their holders. They can come loose and let the accelerator hang up. Make sure every things plugged in, all vacuum lines on and (if it has one) your juice can vacuum reservoir is not rusted out.
    I have in the past used my dremel and a (fine) cut off wheel to make a slot in the back of the throttle stop screw(on the throttle body). This way I could have an idle while I sorted out what was wrong
     
    Last edited: Feb 18, 2006
  5. Sawboy

    Sawboy PlowSite.com Addict
    Messages: 1,591

    I'll 4th the opinion. Get a new IAC. Common problem.
     
  6. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Most times it is the IAC, they like the ignition module tend to die on a regular basis.
    Just change it, if it's not the problem you have to go on a bigger safari to find the problem.
    But the other things I mentioned can be factors in a poor / inconsistent idle. He did mention that it tends to do it when it warms up a little. Before that it will idle. The check engine light just comes on as it dies,that's just telling you the engine quit,if it threw codes it would stay lit.
     
  7. JohnsonLawn

    JohnsonLawn Member
    Messages: 78

    Well guys, today I went out and started the truck and let it run for about 10 minutes and it seemed to idle fine. I pulled out of the driveway and got about 100 yards down the road and it starts to idle rough again and the check engine light comes on. When the light is on it idles very low for a little while then dies. I will change the IAC is you think that is the problem and let you know. Thanks for the input.
     
  8. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    The cheap single model manuals that Advance & Auto zone sells have check out procedures for components. Most all you need is a Volt Ohm Meter to check voltages or resistance. A vacuum tester is used for some components too. Another thing to think about changing is the throttle position sensor. It should be on the lower end of the butter fly shaft.
    Held on with two screws. You have to take off the butter fly assembly to get to it. If all else fails at least these very important parts have been replaced,so they don't die on you later.
     
    Last edited: Feb 20, 2006
  9. Mike F150

    Mike F150 Junior Member
    from maine
    Messages: 5

    check for trouble codes to

    to see how see www.fordfuelinjection.com, you dont need any special tools. You may have trouble codes even without a check engine lite on.
     
  10. JohnsonLawn

    JohnsonLawn Member
    Messages: 78

    I would like to thank all of you guys for your replies. I finally changed the IAC today and what a difference it made. It idles like a new truck, not even a spudder. Hard to believe such small part can impact the way a vehicle runs. This truck has 248,000 miles and still going strong. Thanks again, if I get into a bind again, I will let you know.
     
  11. Sawboy

    Sawboy PlowSite.com Addict
    Messages: 1,591

    Thanks for the update!
     
  12. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    9 times out of 10 it is the IAC. I have replaced them twice on the last two trucks. If you start having problems again consider changing the throttle position sensor too. They tend to go after the IAC's changed. If it idles high sometimes check your cruse control cable, they tend to pop out of their retainer and do not let the butterfly close fully.
     
  13. JohnsonLawn

    JohnsonLawn Member
    Messages: 78

    Mick, where is the throttle position sensor located. Just in case I need to replace it. Thanks
     
  14. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    It's on the bottom end of the throttle butterfly shaft. You have to take off the short section of intake with the butterfly assembly in it.They sell a gasket for it. The sensor is held on with 2 Phillips head screws.The screw slots stripped out as soon as I tried to get them out! I had to take the dremel with a cut off wheel and grind flats on the screw heads. I used an ignition wrench to then get them out.
    A sticking EGR can cause an uneven idle problem too.