Help me create the "Surging Idle Checklist"

Discussion in 'Fox 5.0 Mustang Tech' started by jrichker, Apr 10, 2005.


  1. dwhiskie

    dwhiskie New Member

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    I mounted my aftermarket iac upside down,no more surge
    #21
  2. crunchie12268

    crunchie12268 New Member

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    Wow, why would that work?
    #22
  3. dwhiskie

    dwhiskie New Member

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    Dont know,but I read either on this forum or the corral that some aftermarket iac need to be mounted upside down,It worked for me so I`m leaving it that way and I tried everything
    #23
  4. Ranchero5.0

    Ranchero5.0 The Voice of Reason

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    A little dragon slaying lore here:

    99% of the time on a cammed car opening up the divider between the ports on the IAC with a dremel so the motor idles at 1000rpm with the IAC unhooked, the throttle plate shut and the TPS at .98vdc fixes all surge related problems. Found about to do that on my '93 with a very mild cam and good induction it didn't like idling below 900rpm. The IAC can't react quick enough to a lopey cam induced RPM fluctuation so instead of dampening the surge it increases it. Every E cammed car I've ever worked on needed this to keep a stable idle. Similiar to Fords idle bypass plate without the cobbled look.

    If that doesn't do it check the 12vdc to the heater on the O2's. One smack of wiring on headers wipes out the fusible link hidden in the wiring on the engine side of the firewall where the main puter harness goes through. This will cause the o2's to slowly go out of tolerance and the puter flips out. check this if the car's running really rich a idle too. Ranchero got nailed when first installed and the '93's done it too. I actually ended up soldering on a stereo inline fusible link and installing a 20a fuse to make the repair quicker.

    More to come as I get time...

    Jamie
    #24
  5. dwhiskie

    dwhiskie New Member

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    So,do you mean completely remove the divider between the ports or just make them bigger? My car wont idle below 900 and would like to get it to around 800.
    #25
  6. Funanin

    Funanin Founding Member

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    would replacing the vacuum lines with rubber hose that is rated at 15 psi +/- cause a surge if my vacuum pulls at -17.5 psi at idle?
    #26
  7. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Vacuum is measured in inches of mercury, 30 inces of vacuum = roughly 15 psi. Hose designed for pressure will generally carry vacuum with no problem. Vaccum would try to colapse a hose with no reinforcement by sucking it flat, like a soda straw stuck in the ice cream in the bottom of a milk shake.

    With this in mind, the cause of your surge is not the rubber hose.
    #27
  8. Ranchero5.0

    Ranchero5.0 The Voice of Reason

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    D, I just dremel out a little at a time till it idles around 1k. In my experience the stock puter doesn't like to idle a cammed car down low.

    Jamie
    #28
  9. dwhiskie

    dwhiskie New Member

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    So basically the 950 or so idle I have is about the lowest Im gonna be able to get it right?
    #29
  10. dvs bullet

    dvs bullet New Member

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    Just wondering how much vac. does a stang pull? by the way this a great idea, I have had this prob. for a long time, and this is giving me a lot of potential solutions.
    #30
  11. southbronx

    southbronx New Member

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    Once you have all the checklists done up, have them as a sticky on page one. :hail2: Make it a one stop shop before a "this-has-been-answered-already" question gets posted. :spot:
    #31
  12. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    A healthy engine with a stock cam will pull anywhere from 16"-19" at 675-750 RPM. Changes in spark advance, camshaft timing, and overall engine health will make this figure vary greatly from one engine to another.
    #32
  13. dvs bullet

    dvs bullet New Member

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    Thanks man! :nice: It will give me more ammo when I go after my car with this list :hail2:
    #33
  14. Snake1

    Snake1 Founding Member

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    If you have R12 in your A/C you might want to check the charge on your A/C.
    Low Charge = hunting idle
    unplug your commpressor and see if it makes a difference.
    did with my 88 GT and it went to a steady 650 rpms.
    Decided to take the A/C out,got rid of everything except the compressor(I use the compressor as a pulley only,that way I didn't have to change the belt)
    I've had a steady idle ever since I took everything out.
    I also run with a vacuum guage and that is also running steady at idle.
    Gained on horsepower and fuel mileage.
    #34
  15. 88GTsocal

    88GTsocal New Member

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    Only possible if the hunting idle only happens when the A/C is on.
    #35
  16. Snake1

    Snake1 Founding Member

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    as you probably know Ford heaters are on all the time except when in the off position,doesn't matter is the A/C is on, or heater side is on because your Compressor kicks in on heat side also.
    Put your lever on mix on the heat side and go watch your compressor kick in, Trust me i've been thru all of this with my 88GT and R 12. if it doesn't kick in,not enough oil in your system to activate it.
    #36
  17. 88GTsocal

    88GTsocal New Member

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    I could be wrong, but I'm almost positive that the compressor turns on in the A/C positions and defrost. Not in any of the other positions.
    #37
  18. Snake1

    Snake1 Founding Member

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    On the heat side, the compressor kicks on for a bit then kicks off,on the ac side it stays on until you switch over to the heat side,then it starts its on/off cycle again
    #38
  19. gregpro50

    gregpro50 New Member

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    If you have the original IAC motor on a higher mileage car the idle hunting seems to be a common problem. I have found that simply pulling off the IAC motor and hosing it out with cleaner helps it out a lot. My '90 vert that I just got this year had this problem so bad that it would actually stall. I cleaned out the IAC motor and now it idles perfect. I'm sure this isnt a permanent fix and that it needs to be replaced but it works for now.
    #39
  20. 89MustangGX

    89MustangGX I have nothing productive to add!

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    I've never seen this before, not on any of my Fords ... and the A/C has worked fine.

    As mentioned above, the A/C only cycles on with A/C and Defrost. It does cycle when it's on however, that is normal.

    It sounds like maybe you had a stuck clutch in your compressor or something else going on. :shrug:
    #40

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