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MALFUNCTIONING IAC???

Discussion in 'FAST Support Forum' started by 78 F150, Aug 9, 2018.

  1. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    I have the FAST EZ EFI 1.0 and I’ve had it since 2012. Ever since I’ve owned it I’ve had an issue with the engine stumbling and sometimes stalling when I push in the clutch and let the engine come down to idle. A few months ago I was advised to adjust the IAC from where I had it set (15-20 per the instructions) down to 05. Once I adjusted it to 05 it seemed to solve my stumbling problem.

    However, I still have a problem I need some advice. I have my IAC set at 05, but it doesn't always stay at 05. For some reason, after firing it up from a cold start, the IAC runs around 15-20 (once it is warmed up) and then sometime later after driving it for a few miles it will adjust itself and run at 05. When it’s running at 05, it runs perfect, but when it’s running higher then I have problems with the engine stumbling.

    My question is why is the IAC sometimes running higher than what I have it set at? Do I have a malfunctioning IAC? What’s causing this issue? I'm tempted to buy a new IAC, but I don't want to spend + or - $100 for nothing and it doesn't solve the problem. So I thought I'd get some expert advice first. Thanks for your help.
     
  2. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    Using the control menu? I adjusted the set screw on the TB linkage, which adjusts the IAC count. Am I misunderstanding you?
     
  3. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I have mine set to be in the 5-10 iac count range and it doesn’t get there until completely warmed up. And it fluctuates by a few counts every time I push in my clutch, sometimes it comes to rest at 06 sometimes it will settle out at 08. Also when my fans kick on it jumps up to the high teens. Iv also noticed going one tenth richer on idle af will help a lot with idle dipping at stops.
     
  4. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    My idle a/f is set at 13.1 right now and I've had it clear down to 12.5 and everywhere in between and the stumbling problem is still there if the IAC is running 10+. When it settles down to 05 range (maybe a couple numbers higher just like yours), it runs perfect. Makes me wonder if the IAC is getting stuck or something. Is this possible? Is there any troubleshooting tests I can do on the IAC to see if it's working properly?
     
  5. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Mine was real bad about coming to a stop and idle dipping before I switched to a resistor style spark plug and super conductor wires.
     
  6. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    He just said it goes away when he lowers the iac count enough? But is having a problem of the iac bouncing around from where he set it.
     
  7. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    That's good info. So I'm using Autolite copper core wires #3924 and Ford Performance Parts spark plug wires (p/n M-12259-R460 from Summit Racing). They have a spiral-wound suppression core. Here they are if you want to look at them https://www.summitracing.com/parts/fms-m-12259-r460 . So are these plugs the same as what you are talking about? Do you have a part number for your plugs?
     
  8. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    Yeah, I'd like to lean out the idle a/f ratio, but I need to get this stumbling issue resolved. I using the FAST fuel pressure gauge and it's set at 43 psi (without the engine running). When I fire up the engine, it's around 38 psi or so.
     
  9. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I believe your plugs r resistor style and looks like your wires are comparable to the msd super conductors. So I think your good to go there. Also to help ease your mind my pressure gauge is set to 43psi engine not running and is about 38 psi engine running. R u sure that your not seeing the higher iac count while the engine is still trying to get up to full temp or do u have electric fans or ac?
     
  10. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    No, I'm seeing the higher count after it's warmed up. The last time I drove it, I drove it for a few miles around town before the IAC count came down to 05. I have a 92 Mustang GT 5.0L and the IAC on that car has given me problems in the past and I took it off and cleaned it, put it back on and it run fine. Then it would get dirty and gummed up again and I've have to clean it again. Is the IAC on the FAST throttle body something that can be cleaned like on my Mustang? I know it's a GM IAC and it looks a lot different than the one on my Mustang. Maybe cleaning it would help?
     
  11. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I had a hard one finding ohm info on those wires. One site said 1000 like u found AA but I also found another site that said 40 ohm per foot for those wires.
     
  12. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    Well I’m sure you will notice a big difference switching to the better wires. I was running 500 ohm wires and it made a huge difference on my car when I switched to the 40-50ohm wires.
     
  13. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    AA--Sounds like the best place to start is replacing the plug wires. I think I'll try these https://www.summitracing.com/parts/msd-35389/overview/ . It advertises 50 ohm/ft. These should work, right? Yes, I have a 460 in my truck with Ford Racing Super Cobra Jet aluminum heads. I am also running an Edelbrock Torker II single plane intake. I've had this stumbling issue from day one that I've owned this EFI system and these are the same wires I had when I built the engine. So maybe this is the cause of my stumbling problem. However with that said, it is odd that when my IAC count is running at 05, the stumbling problem goes away. Correct me if I'm wrong, but if the wires were the problem, wouldn't I still have stumbling problems even with the IAC count running at 05? Seems logical to me, but who knows.

    Fishhore--you stated you noticed a big difference switching from 500 ohm/ft wires to 40-50 ohm/ft wires. Exactly what problems were you having with the 500 ohm/ft wires? And I assume the 40-50 ohm/ft wires solved your problem???
     
    Last edited: Aug 11, 2018
  14. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I had problems fouling plugs, and wanting to die when coming to a stop or coming to an idle after revving the engine. Changing my plugs and wires to more efi friendly ones made the biggest improvements for me. I still have on small issue of a slight misfire out the exhaust at cruise but I can’t pin it down yet. That is my only issue and most ppl might not even notice the miss, every other aspect is great from cold starts wot it’s great. But everything got better when I switched. I think if they put in big bold letters on the box to have resistor plugs and 50ohm or less wires there would be a lot more happy ppl. The only reason my iac count is down around the 10 range is because when my fans kick on I will start to dip a little when coming to a stop if I have them up at normal level
     
  15. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    I'm liking what I'm hearing. Sounds like you had the same problems I'm having and the plugs & wires solved the problem. This is giving me hope I can finally get this issue resolved after years of fighting it. I think I'm going to try this first before throwing money at a new IAC. But I'm going to pull the IAC off and see if I can clean it (if it needs it) and do an ohm test on it to verify it's working correctly. It just doesn't seem right that sometimes the IAC count will be higher and other times it will run where it's set at. Logic tells me there's a problem somewhere

    Someone mentioned to make sure to use the factory spark plug gap. The problem with that with my setup is that I'm running an MSD 6A ignition box with a MSD adjustable timing control and the instructions state to go with .050-.060 gap, which is larger that stock (stock = .044). So I went in between at .055.

    I agree with you, they need to make sure this spark plug & wire information is highlighted and made know how important it is to a properly functioning EFI system. Yes, they do mention it in the instructions, but it's not emphasized how important it is.

    I'm not running an electric fan, so I don't need to bump up my IAC, but I do want to add one sometime in the future.
     
  16. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    So let me clarify and see if I understand you correctly...

    1. You advise that I use the factory plug gap, correct? Which is .044 for a 78 460. Or are you saying to leave them at the gap they are set at from the auto parts store?
    2. You are advising that my Autolite #3924 plugs are too hot of a plug for the heads I'm using and I need to go one stage colder?

    I'll definitely do a new tune once the plugs & wires are installed. You mentioned I might have to reset it two or three times before it clears. Question.....how long do I run the engine with a new tune before I clear it again?

    Regarding the MAP reading, does it matter if the engine is cold or up to operating temp? Just as long as the engine is not running? I just went out and checked the MAP reading on a cold engine and it's at 97. I'm at 794' elevation. Shouldn't that read 100???

    The FAST instructions state my idle A/F ratio goal is anywhere from 13.0 to 13.5. You mentioned my 13.1 setting is a little rich. Should my goal be 13.5?
     
  17. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    My current a/f ratios are set at: idle = 13.1, cruise = 14.3, wot = 12.7. I'd like to lean out the idle and cruise as much as possible, but I don't think I'll mess with it until I get a few miles on the new plugs & wires and see how it acts. I'll do as you advise and reset the tune 3 times then fire it up and head out for a drive and see what happens. I ordered the plug wires from Summit today and should be here this week sometime.
     
  18. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    I'm not sure how the plugs look. They are new and I don't have 100 miles on them, but I haven't pulled them yet to check them. I've had another issue I've been fighting besides the engine dying that I've been trying to resolve.

    I upgraded to the new digital handheld in February 2018 and every since I've owned it it keeps disconnecting from the ECU and throwing codes. Sometimes it throw codes and sometimes it doesn't. But when it does it throws codes to every single sensor on the code screen except for one. When it does this it puts the system into limp mode and prevents the engine from running under full power. When I clear the codes the engine runs normal again. I never had this problem using the old analog handheld controller and I've owned this system since 2012 or 2013. It's only been doing this since I installed the digital handheld. I've had the ECU and the digital handheld tested by Comp Cams and they say there's nothing wrong with them, but obviously something's wrong somewhere. Last time I sent it to them to test, they sent me a different cable to connect it from the ECU to the handheld thinking there's a problem in the wiring. I just got that installed last week, but haven't driven it yet so I don't know if the problem is resolved. I'm not going to drive it until I get the new wires and plugs installed later this week.

    Question.....if after installing the new wires & plugs you think the idle a/f will like a 13.7-13.8 range, should I set it at that ratio after resetting the system with a new tune? Or start at where I have it now at 13.1? I'm thinking of setting it at 13.7 to start and see what happens???? I do know the exhaust pipe is black, which tells me it's running rich, but like I said I've had this stumbling/dying issue since I've owned the system and I've adjusted the a/f ratio all over the place over the years trying to resolve this stumbling/dying issue. I suspect it's been running rich all these years and the plugs are usually black every time I change them. I'm really hoping the wires solve my issue so I can finally get this system tuned properly after years of frustration of it not running properly.

    Question....If I go with one step colder plug, how will it effect performance? How does a plug that's too cold effect how an engine runs? What are the characteristics or symptoms I will notice? How do you tell if you need a hotter plug? The reason I ask is because you're suggesting I go with a colder plug than what Ford recommends, so I'm just wondering how the engine will respond to this change.
     
    Last edited: Aug 12, 2018
  19. 78 F150

    78 F150 Member

    Joined:
    Feb 6, 2013
    Ok, that makes sense (colder plug explanation). I'll set the idle a/f at 13.5, cruise I'll set at 14.3 and wot at 12.7 and go from there. However, the default wot setting is 12.8. Does it matter if I set it at 12.8 or 12.7? I might just leave it at the default setting.

    Yes, FAST updated my ECU the last time I sent it in with the handheld to be tested, which was earlier this year. So I have the latest update/program. So that shouldn't be an issue. Now if I can just get it to stop disconnecting and throwing codes and putting my engine into limp mode, I'll be happy with the digital handheld. It's been nothing but problems every since I've owned it.

    FYI...thank you (and everyone else) for your help. I'm finally having a positive feeling that I might just get this stumbling/stalling issue resolved finally after fighting it for years. We'll see what happens.
     
  20. fishhore

    fishhore Member

    Joined:
    Aug 15, 2014
    I would do a reset and just leave the afr’s where they reset to for now. I know on my car if I go any leaner than 13.5 idle afr then my rpms will start to dip when coming back down to idle while stopping. Just get the new wires and plugs on, do a reset on the tune and then set your iac between 5 and 10 counts on the master screen after it’s warmed up, then do a tps calibration and go for a drive.
     
    Last edited: Aug 12, 2018

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