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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. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    If the IAC is bad, most likely, you will not be able to raise it up and down smoothly using the menu control.
     
  3. 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?
     
  4. 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.
     
  5. 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?
     
  6. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Yes.
     
  7. 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.
     
  8. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    13.1 is very fat for pump fuel. Be sure the fuel regulator is supplying 43 PSI to the injectors in neutral.
     
  9. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Idle dipping with clutch application is common when there is excessive end to end crankshaft play. This is mostly seen in cases of reground crankshafts, but can be caused by a worn or improperly sized thrust bearing.
     
  10. 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.
     
  11. 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?
     
  12. 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.
     
  13. 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?
     
  14. 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?
     
  15. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Those wires are a problem. FAST recommends at least 150 Ohm per foot wires, but most have found 50 Ohm or less per foot is better at preventing interference with the ECU. These are 1000 Ohms per foot! I use MSD Superconductor spiral core wire @ 50 Ohms or less per foot. I also prefer their hi-temp race boots over the standard silicone boots - so I build my own wire sets using their di-electric grease.

    I use NGK standard copper core resistor plugs without anti-seize (NGK doesn't require anti-seize and it will cause problems). You'll need the factory heat range or one range colder than factory for your engine. NGK can and will advise the correct factory plug in their copper V-core series for your engine. Also, do not change from the factory gap the plugs come with or you will upset the plug heat.
     
    Last edited: Aug 11, 2018
  16. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Verify the analog gauge accuracy with the handheld. 38 does sound correct running under no load.
     
  17. 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.
     
  18. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Added note: Using cheaper wire sets will cause stumbling and fueling issues with computer systems. Ford Performance advises these are 1000 Ohm per foot. They know their product.
     
  19. 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.
     
  20. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    The plug wires you mentioned indicate you have a 385 series engine. If you do not have a single plane intake, it will cause TBI problems due to fuel reversion. This reversion does cause un-equal cylinder fueling among other problems. For your pickup, I recommend the Edelbrock Victor.
     
    Last edited: Aug 11, 2018

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