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Thread: Understanding Idle Control: 11-20 Mustang GT

  1. #1
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    Understanding Idle Control: 11-20 Mustang GT

    Hi Guys,

    It's been a while since I've been on here but I experienced some issues recently on a few cars where they seem to behave with an odd idle, and I wanted to collect some information on understanding the closed loop idle on the Mustangs and how to tune it properly, if possible.

    For instance, what exactly controls the closed loop idle, what tables give the guidelines for it to follow. Setting a setpoint for the idle obviously controls which RPM targeted, but what controls the throttle blade to maintain a position and what adjusts the timing to stabilize the idle?

    There are a few tables in question (2017 Mustang GT w/ MT-82):

    Idle Airflow > ETC Idle Throttle Angle: The table reads airmass vs throttle angle. Assuming that this is a given airmass window to have an expected throttle angle for the airmass. Does adjusting it actually do anything?

    Idle > Torque > Feedback, Proportional, Integral, Idle Torque Reserve, Decel Torque: Assuming the torque based PCM gives an allowable/ expected torque target at idle, and it uses this and the ETC Idle Throttle Angle to control the closed loop idle?

    Issues Experienced Recently:

    I have seen a few cars, after some modifications are performed, that seem to have some difficulty with the closed loop idle. Idle rpm targets usually are bumped for the modifications to aid the closed loop idle, but what seems to be reoccuring (Not all cars, two cars with the same mods, one will have issue and another won't) is the idle will increase and decrease rpm while sitting still idling. Spark advance would be ideal to remain at 12-18 degrees, however the spark advance will remain constant at the desired amounts, then increase somewhere to the neighborhood of 40-42 degrees of spark advance. When this occurs the idle drops with it, taking the trims with it. It will consistently increase and decrease timing, what appears to be hunting. When this occurs the idle drops and then increases back up, in some cases it attempts to stall out the car.

    99% of the cars I've seen that this happens, timing hunts but the idle remains +/- 50 rpms on target and the timing jumps just makes the exhaust sound a little funny. However, the car I dialed in yesterday, would almost stall most of the time and in some cases, would actually stall out. I attempted lower rpm targets and higher rpm targets, adjusted the ETC Idle Throttle Angle table slightly closer to the airflow it was seeing, nothing mattered.

    I'd like to understand how the system works so that I can fix it if this ever occurs again and moving forward to make sure these cars remain with good idle quality, as this is literally the first thing people experience when starting up their vehicle, not a good first impression if it has issues.

    Kris

  2. #2
    im having the same issue. mine is a engine swap. gen 2, 2.9whipple, return fuel, ID1050x, e85. I just notices my fuel just showed cl-fault.

    log mach1e85trying to fix rolling idle.hpl

  3. #3
    I was chasing an idle issue for the longest time on my 13. It is a 100% stock junkyard pull coyote.
    To make a long story short, my load calculations were the root cause. I had idle undershoot issues, occasional stalling and surging. Along with that, throttle response was like a light switch.
    The biggest contributor was my final drive gear ratio, and transmission gear ratios. I had to set final drive to 1.8 and I have 3.73s to get the speedo correct. Once the gear ratios were corrected, it cleared up 95% of the issues.
    I was able to almost totally fix the idle before the gear ratio correction by pullin 8* of global timing as a temporary fix.

  4. #4
    ill look into that tonight. I'm sure I'll have questions. Thanks

  5. #5
    Make sure you're not chasing your own tail with idle learn. Clean the throttle body and make sure its closing all the way and disconnect the battery and do the idle learn if it's still out of whack then make the adjustment in the tune

  6. #6
    JuiceNA when you say load calculations was the root cause and then say changing your final gear ratio made the biggest difference.

    Wouldn't that have an effect on idle when coming to a stop? my idle issue happens when starting and letting engine idle.

    By the way I have not had a chance to adjust anything. I hope to get to it tonight.

  7. #7
    I thought I had two separate issues. Idle stability and excessive knock. PCM was commanding 0* if I just steped on the throttle in high gear just to pick up speed. And car would not pull at all.

    I did not have software at the time, only my x4. So I went and pulled 8* global timing as a test. It did infact help with the knock, but to my surprise, it also fixed my idle issues. Stumbled on it by sheer luck.

    So my deduction from all this, the pcm was looking in the wrong tables for data, as the load calculation was not correct.

  8. #8
    yesterday night I adjusted o2 delay on a 2017 5.0 mustang after installing long tubes. when added to the o2 delay the idle would start to roll. I read in another thread that murfie suspected that the o2 delay doesn't actually do what its believed to do. im starting to think that's true.

  9. #9
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    Quote Originally Posted by Jcbryantllc View Post
    yesterday night I adjusted o2 delay on a 2017 5.0 mustang after installing long tubes. when added to the o2 delay the idle would start to roll. I read in another thread that murfie suspected that the o2 delay doesn't actually do what its believed to do. im starting to think that's true.
    That is very interesting. Murfie and I have discussed a lot in the past, dude is a genius. I'd believe anything he states.

    Kris

  10. #10
    Fixed my rolling idle by changing transport delay back to stock!

  11. #11
    Tuner in Training
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    Jun 2019
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    i was gonna post a thread about the same issue..

    my idle afr is jumping around sometimes especially once the car is warm and in traffic or parked in the garage.

    at first i started blaming my PMAS intake since that thing is huge comparing to the other intakes in the market, and i have tuned several cars with JLT intakes with no issues at all.

    i'll do the transport delay test and i'll post the results.

  12. #12
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    Aug 2019
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    I see similiar things at idle with the spark jumping around a bit so I just tried to load up the stock transport delays to see what would happen. It does change something but the overall pattern stays the same for me. Luckily, the car idles and doesn't stall but it's clipping in and out of something.

  13. #13
    Same issue for me, mine has gotten better as I adjusted the torque tables in the idle are for that mapped point, that said if I lower the values much from where they are the car pulls timing to keep the 800 idle, it can go from 1-2 degrees to -5. That heats up my heads and valves so I added to the tables. This ensures I have at least a couple degrees of positive spark but I still avg from 2-7 degrees. Raising values any higher gives ipc error. I think the car needs a bit less air, ie load but the MAF and SD should be about spot on. I wonder if I need to adjust friction torque losses or maybe some temp comp tables a bit. Might lower DD table slightly.

  14. #14
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    I had the same problem, I solved it by adjusting the throttle.

  15. #15
    Which table and cal did you use, I have not messed with any TB tables as I assumed they were correct, I have considered adjusting the idle airflow parameters which are currently at 10 percent. I am assuming probably incorrectly that I can make the ecu see a higher cylair value, just at idle and Maybe close the TB just a bit and raise spark.