Idle surging

Discussion in '2005+ Ford Mustang v6 4.0L Tech' started by DarrenN, Jan 21, 2022.

  1. DarrenN

    DarrenN Junior Member

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    So my issue has been a little bit of an ongoing one for a while and so far I've replaced the below list of parts due to various codes and misfiring issues etc when I first got the car along with general maintenance. Its all stock so nothing questionable done to it as far as I know!

    Its a 2007 V6 4.0 5 speed manual and while driving my idle speed will sit at around 750 rpm for most of the time when I stop, but randomly it'll rev up to 2000rpm + when I'm at a stop sign or lights or when I push the clutch in before it settles back down again to a lower number. Sometimes if I've stopped somewhere and turned the car off then started it up again for the rest of that trip it behaves normally, so it does seem to be pretty intermittent!

    When replacing the throttle body I ran through the idle relearn procedure from the manual as usual, and for that trip - a near 40 mile drive with speeds from 20mph - 70mph it ran perfectly so I was hoping it had settled down but two days later on a drive it started randomly revving again!

    Any ideas on what I can try to solve this problem or has anyone noticed it on their 4.0?

    Parts replaced:

    Throttle Body
    Battery
    Spark Plugs
    O2 Sensors
    Leads
    Coil Pack
    TPS
    EGR Valve
    Fuel Filter
    Oil & Filter
    Air Filter

    Hopefully there's someone out there who has had similar issues to this and can shed some light!

    Thanks

    Darren
     
  2. Juice

    Juice forum member

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    You need to datalog idle to see what drives the flareup.
    New TB, did that i clude new electrics?
    Idle relearn is basically letting it idle. Reset pcm (scan tool or batt disconnect) start it cold and let it idle till the cooling fan comes on.
    Did you scan for codes? There should be idle related codes atleast pending. If not, it sounds like a huge but intermittent vacuuum leak, which is odd.
     
  3. DarrenN

    DarrenN Junior Member

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    Yeah next up will be checking the live data, hopefully I'll get time at the weekend but so far it's not thrown any codes at all since the misfiring issue was fixed with a new coil pack, plugs etc. I've had it tested for a vacuum leak too which was my first guess... no apparent issue there according to the garage. It's really odd and a pain in the ass trying to chase down such a weird issue with no apparent cause!
     
  4. Juice

    Juice forum member

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    There IS a reason, just need to find it.

    Can your scan tool read pending codes? Some dont. A pending code needs to mature before the CEL comes on.
    I think only one of my apps can read pending codes.
     
  5. DarrenN

    DarrenN Junior Member

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    I believe my scan tool can read pending codes - all the previous codes I've fixed haven't triggered a check engine light at all. I've got a scanner coming today that will read the live data so I'm hoping that'll be more in depth to what I've currently got.
     
  6. Juice

    Juice forum member

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    You need Forscan with elm327 (usb preferred, wifi is ok, never tried bluetooth)
    There are codes that will not throw a CEL.
    The one scan app I have lists all 3 code categories: current, pending, and permanent. Most tools seem to only read and clear current codes.
    Permanent codes clear themselves after the problem is repaired.
     
  7. DarrenN

    DarrenN Junior Member

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    Ok will check it out, thanks. What scan app have you used for finding the 3 code categories? I'm using an iPhone
     
  8. Juice

    Juice forum member

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    Dash command is the only app that I have that reads all 3.
    Not sure if Forscan does, I am thinking NO. But it has the best live data viewer. Other than SCT live link.
     
  9. DarrenN

    DarrenN Junior Member

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    Ok great thanks I’ll take a look at them and see if anything shows up
     
  10. Lime1Gt

    Lime1Gt Member

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    Have you cleaned or replaced your MAF sensor. Even though an air filter is before it, microscopic dust can sandblast and wear the sensor. It can also be compromised by using an over oiled gauze filter. Check the air tube from MAF to Throttle body for cracks, loose clamps. Wiggle and check all the PCV system hoses and fittings when the surging is happening. If idle smooths there may be a leak in that system. Clean your MAF sensor with CRC QD electronic cleaner or MAF sensor cleaner only.
    With the engine surging, lightly spray QD at the intake manifold areas as well as vacuum hoses and see if the engine speeds up which should indicate gasket or seal leaks. Use caution with no spark sources near by and have a fire extinguisher close. Propane can also be used. I would think a smoke test will show a failed part but maybe not one that's just starting but is affected by the engine vacuum under a closed throttle when running.
     
  11. DarrenN

    DarrenN Junior Member

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    Yep, the MAF sensor was replaced, new air filter etc as in the previous posts so all either new parts or cleaned. I did have a vacuum leak test done which found nothing, when the idle is behaving normally it looks rock solid, the surge isn't like a wobble where it's constant, just a surge increase of upto 2000 - 2500 rpm then back. I've noticed since replacing the throttle body that the idle can sometimes get as low as 500rpm then come back up, but again this is when the odd behaviour is happening, otherwise it just sits around the 750 rpm area. I tested it with live data over the weekend but as you'd expect it didn't do anything abnormal on the test drives so will have to keep trying it until I catch it acting weird!

    Is there anything specific I should be looking for in the live data - any specific are to keep an eye would you guess?

    Thanks!
     
  12. Juice

    Juice forum member

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    When I was chasing an intermittent idle issue, I watched:
    Desired and actual idle speed, idle 'source', coolant temp, actual throttle angle, open/closed loop status. (PID names may be slightly different.
    Coold temp may raise idle if the reading is not accurate.
    Desired idle speed to see if the pcm is actually wanting to raise idle or not. Idle source/mode for same.
    Basically to see if the idle creep is commanded by the pcm or not. If not, that should set a code, and I find it strange that you dont get a check engine light or pending code.
    Is this car tuned?
     
  13. DarrenN

    DarrenN Junior Member

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    Thanks, I'll take another look today and see what I can find.

    The car doesn't have a tune on it now. When the idle issue first showed up I was having the misfiring issues and needed a good few parts replacing. It all settled down after that for a while so we had a tune booked in. A few days before that the idle surge returned but we got it tuned anyway, so it has happened both with and without the tune! We returned it to the stock tune to see if we could chase down the idle issue before playing around with any further tuning!
     
  14. Lime1Gt

    Lime1Gt Member

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    A couple of other suggestions. is a/c clutch cutting in and out when surging? Carbon build up on intake valves with higher mileage.
     
  15. DarrenN

    DarrenN Junior Member

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    No, I don't think there's any cutting out when the engine does surge, the car has just over 70k on it so not a massive number compared to some!

    I ran through some different apps and found an old archived/inactive 'trouble code' & and ECU Engine manufacturer fault, but after checking a 2nd time the ECU flat code was all green and not reporting an issues. I've added a couple of pics from the app screen. So far (typically) when I've been checking it it's not returned but will check through again as I drive it. IMG_6071.PNG IMG_6072.PNG
     
  16. Juice

    Juice forum member

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    The battery volts low is interesting, and may point to the alternator. Pcm maybe raising idle to compensate for low system voltage. A possibility, monitor voltage see if it is low when idle rises.
    Need more detail on the manufacturer code, to see if it is something that needs to be addressed.
     
  17. DarrenN

    DarrenN Junior Member

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    Interesting you mention the alternator, it had crossed my mind as I've had some funky electrical things happen - for example when the car is warmed up if I pull over and restart it the idle issue goes away. This has only happened once, but driving along suddenly the engine cut out completely - that's not happened for a while though. I seem to remember testing the alternator output a while back and although it was on the low end of the Voltage readings it was in recommended levels, but that was also after having driven the car for a few hours the day before... Hmm interesting!
     
  18. Juice

    Juice forum member

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    Charging system threshold is set at 12v before the pcm throws a code and shows dash warning. (On the coyote anyway) Im sure that threshold is a standard across most cars.
    Does not explain car cutting off.
     
  19. DarrenN

    DarrenN Junior Member

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    Yeah thankfully that car cutting off thing has only happened once! I'll check over the voltage monitoring when I can get the surging issue happening again. Generally happens after the cars been sat around for a couple of days and until it warms up (and I can pull over and restart) it'll keep acting up. So fairly predictable when it does do it.
     
  20. Mustang Sue

    Mustang Sue Junior Member

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    Throttle by wire that regulates idle is used so you don't have an IAC like my 2002 Mustang. Electronic throttle control.
     
    Last edited: Jan 27, 2022
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