Cold Blooded Fi, Acts Like It Needs Choked

Discussion in 'Fox 5.0 Mustang Tech' started by 7991LXnSHO, Apr 27, 2013.


  1. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    My 91manual 5.0 has ported stock parts, lots of bolt ons, #24 lb injectors, and a FMS letter cam (E?). I checked that the timing is advancing with the Spout plug in. It has Ford fuel injection, but it acts like I need to pull the choke out until it is warmed up a bit. For the youngsters, that means a baaaaad idle and it is likely to die without more foot feed until warm. After it warms up some, it runs and idles fine. Does anyone have good ideas for this quirk or is it the big cam? I know of no one within a three hour, one way, drive for a chip and dyno tune. I know what to do for a Holley, but that does not apply here.
     
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  2. mikestang63

    mikestang63 Mustang Master

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    What is your fuel pressure set at with the vaccum line off the FPR show? 38-40 is within range. What is your timing with the spout plug out. 10 BTDC is stock. You can go 14-16 if you run 93.

    Is it 24 lb injectors or 42?
     
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  3. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    Oops, I think auto correct got me. They are 24 lb with a matching MAF, set at 39 PSI. Timing is 14 btdc, 10 idled so rough I did not leave it there. It did this with the factory MAF and 19 lb injectors and a higher psi. The PO had it warm when I got to first see it "fresh from the car wash".
     
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  4. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    The only codes are related to the new smog parts that still are waiting to be reinstalled with new cats. The surging idle checklist made it run well warm.
     
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  5. ratio411

    Founding Member

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    You have a problem that is common with alphabet cams in cars that do not have the ECM tuned.
    You have a few options...
    *You can drill a small hole in the throttle blade to create a small air bleed, then hope that when the engine warms up, the IAC compensates and does not make it idle higher when warm.
    *You can add a Ford IAC adjuster plate, with a built in air bleed that you can adjust with an allen wrench.
    *Tune the ECM.

    You also should check to see that your IAC is working.
    You might be running purely on the throttle settings, and not have IAC support.
    It is possible to do, but you don't have the convenience of the IAC when the engine is cold, or under heavy load when at idle...

    Also, if the car was not set up by you, see if the previous owner, or builder, put in an IAC restrictor plate/gasket.

    I would start by making sure the IAC was even working.
    Good luck!

    Oh, and the part about the car running badly at 10* advance when timing with the SPOUT out, is not right at all.
    I would also check that out...
    My prime suspect there would be the IAC as well, but if that's not it, you need to look in that direction.
     
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  6. ratio411

    Founding Member

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    Do you have a "U-pull" yard near you?

    If so, take advantage and look for an EFI Ford truck from around 87-89, and look at the IAC.
    If there is a thin metal plate between the IAC and TB, that is the idle adjustment plate.
    Ford had a recall on their early EFI trucks, due to idle issues, and they installed this plate on a great many trucks.

    You could buy them at the dealer until very recently for just a couple bux. They were discontinued by Ford, and now those that bought up the unsold supply are selling them from anywhere between $40 and $80 bux!
    So this is just a heads up that you can find them in the junkyards for next to nothing.
    I pick up every one I find. I can't remember ever even being charged for one, they are so small and worthless appearing.

    Here here is one put to use on an HO engine:
    [​IMG]
     
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  7. jrichker

    jrichker StangNet's favorite TOOL
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    Did you do the base idle speed adjutment proceedure?


    Recommended procedure for cleaning the IAC/IAB:
    Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. Take the solenoid off the body and set it aside: the carb cleaner will damages some types of plastic parts. Soak the metal body in the carb cleaner overnight. There is a basket to set the parts in while they are soaking. When you finish soaking overnight, twist the stem of the IAB/IAC that sticks out while the blocker valve is seated. This removes any leftover deposits from the blocker valve seat. Rinse the part off with water and blow it dry with compressed air. The IAC/IAB should seal up nicely now. Once it has dried, try blowing through the bottom hole and it should block the air flow. Reassemble and reinstall to check it out.

    Gunk Dip type carb & parts soaker:
    [​IMG]

    Setting the base idle speed:
    First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. If you have a wild cam, you may have to raise this figure 100-150 RPM or so. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s. This figure will increase if you have a wild cam, and may end up between 800-950 RPM

    Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

    This isn't the method Ford uses, but it does work. Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks.
     
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  8. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    Thank you for the well thought out answers. I have set the idle with the IAC unplugged as high as I can without throwing a high idle code. I followed jrichker's and BBK's instructions, and that is why it idles well warm. As far as the IAC functioning, the idle speed is higher in neutal as I coast to a stop sign, then drops to normal after I stop. I have electrical signal going there, and I replaced the IAC when installing a bigger TB. So it seems to be OK to me.

    I had never heard of the Ford idle air plate, but I have seen the aftermarket one.

    I know there can be problems if a carb has the throttle opened too far for idle speed.
    Besides the range of the TPS screw slots, are there any F. Inj. problems from opening the TB blade so far to adjust idle speed up for a big cam?

    As I am not done with changes, I hesitate to chip it or drill it. Cow chips are more common than computer chips here anyway. A Ford pickup in the salvage yard is very possible. Unless there is another cold only issue possibility, I will plate it. I am hesitant to drill a hole in the tb plate when I may be changing the combo. (When I put a ported Explorer intake manifold on, I want to do heads, but I AM doing Rhodes lifters to get some low end back. I had great sucess on carb. cars with them.) And I will follow up when done.
     
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  9. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    I have an extra IAC. What if I 1. slot the face area between the two ports or 2. drill a hole between the two ports? That way I do not have to modify the throttle body? What size of bit should I start with?
     
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  10. 88LX5.Oh

    88LX5.Oh Advanced Member

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    I pretty much have the same issue. It doesn't do fast idle on cold starts like it should. And I know my IAC is working because when I unplug it, idle goes down so low that it almost kills the engine. And as soon as I plug it back up it kicks back up to roughly 800 RPM.
    But I can hop in my '92 Bronco and every time I start it, no matter if it's at operating temp or dead ass cold, it'll do fast idle and depending on temperature it'll only last for a few seconds, or over 30 (when it's cold as hell)
     
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  11. jrichker

    jrichker StangNet's favorite TOOL
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    Do the base idle setting procedure as posted above. Raise the base idle speed setting to compensate for the different cam.
     
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  12. pearlnotchback

    pearlnotchback Active Member

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    I have the same problem and ive tried everything under the sun to fix it with no luck
     
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  13. jrichker

    jrichker StangNet's favorite TOOL
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    The IAB may work great when warm, but just like most mechanical things, it is a little sluggish when cold. Do the cleaning and base idle procedure in this thread that I posted to fix the problem. If the base idle speed is incorrectly set or the IAC sticks when it is cold, the engine stalls or doesn't idle when cold.
     
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  14. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    Original poster here with a question for jrichker. My IAC is new so I did not clean it. Same with the TB and MAF. Any other reason why the IAC might be sluggish while cold? The symptoms sound right. I will check again that I have volts there on vold start up. I usually check things after the car is wzrmed up. Do you have a suggested voltage range I should find across the IAC's terminals?

    Question for anyone - what size hole should I start out with if I go the add an air leak (drilled hole) in the throttle blade or making my own IAC spacer route?
     
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  15. jrichker

    jrichker StangNet's favorite TOOL
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    What were the results of the base idle setting procedure?

    Sorry, a check with a voltmeter won't get you very much useful information, except to check that there is good 12 volts on the red wire.

    Then check for continuity between the white/lt blue wire and pin 21 on the computer. The IAC connector contacts will sometimes corrode and make the IAC not work. The red wire on the IAC is always hot with the engine in run mode. The computer provides a ground for the current for the IAC. It switches the ground on and off, making a square wave with a varying duty cycle. A normal square wave would be on for 50% of the time and off for 50% of the time. When the idle speed is low, the duty cycle increases more than 50% to open the IAC more. When the engine speed is high, it decreases the duty cycle to less than 50% to close the IAC. An old-fashioned dwell meter can be used to check the change: I haven’t tried it personally, but it should work. In theory, it should read ½ scale of whatever range you set it on with a 50% duty cycle. An Oscilloscope is even better if you can find someone who has one and will help.

    [​IMG]
     
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  16. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    It runs fine when warmed up a little. The IAC should be working as it raises the idle when moving in neutral and lowers it after stopped. The TPS is within range.
     
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  17. jrichker

    jrichker StangNet's favorite TOOL
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    Were you able to get the engine to idle at 600 RPM or 700 RPM when cold, IAC wiring disconnected, A/C off, transmission in neutral and the SPOUT out?
     
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  18. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    I do not remember that the BBK instructions I followed last time had me pull the SPOUT plug. (I also do not see it in your instructions above too, could I be going blind?:cool: ) I will try it and get back. It sounds like that would give the computer more timing adjustment leeway at idle.

    As far as the IAC function, I can check the wires and 12 V, but I know of no one with an oscilloscope. I remember I have a spare IAC that does seal. I can put it on, leave the current one plugged in and actually see it function.

    After all this, my car should idle cold just because it is tired of being probed and tested!:confused:
     
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  19. jrichker

    jrichker StangNet's favorite TOOL
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    You are correct, the SPOUT removal and several other steps that are present in the "Surging Idle Checklist” are missing from my post on cleaning the IAC and setting the base idle speed. That was an omission on my part, which I will correct.

    Here's what was missing....

    Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed. Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. A wild cam may make it necessary to increase the 600 RPM figure to 700 RPM or possibly a little more to get a stable idle speed.
    Changing the mechanical adjustment changes the TPS, so you will need to set it.

    When you are satisfied with the results, turn off the engine, and re-install the SPOUT and reconnect the IAC. The engine should idle with the range of 650-750 RPM without the A/C on or extra electrical loads. A wild cam may make this figure somewhat higher.

    My apologies for the omission and any extra work it may have caused.
     
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  20. 7991LXnSHO

    7991LXnSHO Well-Known Member

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    I set the idle with the IAC unplugged AND the Spout out. (I do not think I had the spout out when I set it before - it was not in the other instructions and I missed it in a past post of these instructions.) Having the Spout out made a BIG difference in the setting. After I got the TPS voltage ranged and the parts plugged back in, it wanted to settle into a low idle of over 1000 RPM! I backed the set screw out a bit until it did settle to below 1000 rpm with things plugged in, and it is a smoother idle now. I'll see later if that kicks out a "too high idle" code. With the AC on, it does idle a couple of hundred RPM lower and lopes. But it does not act like it will die now with the AC on. As far as the cold start, it was 80 F this AM. Even with the old settting, there was no cold start issue today. I may have to wait until fall to see if this fixed it, but I bet it at least helped.

    Exactly two weeks ago, we had significant snow. Today it was 102 downtown. The state we live in is a state of insanity this year, not one of the normal 50.
     
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