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Thread: Cold idle RPM gems V8

  1. #1
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    258

    Cold idle RPM gems V8

    Hi all,

    I've been having this problem that my engine usually want's to nearly stall if I try to move the car just a few meters when cold and in various other circumstances. I suspect the idle valve but am not sure how to test it. The first thing that came to mind is that nearly all vehicles I own or have owned have a high idle when cold, that is to say higher then when warm. My V8 has never had a high idle. not even when around the arctic circle at around -30c it's always 650-750 rpm. I thought that was because the V8 with the power strokes so close to each other simply does not need it but perhaps my car is simply broken but I never really noticed

    So how do your P38's idle when cold?

    -P

  2. #2
    Join Date
    Feb 2010
    Location
    Townsville, QLD
    Posts
    2,523
    Mine is a Thor, itíll sit up around 1,100rpm for maybe 30sec before settling down to 700rpm. Some GEMS ones Iíve worked on have been similar. The warm idle on GEMS seems to be a bit lower, around 600 to 650rpm.

    I think yours is special! It should still do the magic high-idle when cold though. Perhaps the IACV needs attention?

    Cheers
    Keithy

    Green 2000 P38 Range Rover HSE - Gone
    Blue 1999 P38 Range Rover HSE - Gone

    Silver 2002 P38 Range Rover HSE - Sequential LPG, BCDC Charger, TPMS, Rear Locker, Wheel Carrier, Bullbar & Spotlights, General Grabber AT2's, Too Much to Mention!

  3. #3
    Join Date
    Jul 2014
    Location
    Sydney
    Posts
    670
    My Thor is the same as Keithy's.
    2000 4.6 HSE Alveston red
    2007 307 xse peugeot
    1974 xj6l jaguar

  4. #4
    Join Date
    Jan 2016
    Location
    Netherlands
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    258
    @keithy, do'nt let my car hear that! It want's enough special attention as it is haha

    In any case, I think it is about time I took that thing apart, yes. I'll do some searching around ofcourse, but does anyone know the best way to test these?

    Cheers,
    -P

  5. #5
    Join Date
    Apr 2009
    Location
    Crafers West South Australia
    Posts
    11,655
    Have you adjusted the base idle speed up? This is done by the screw set into the top of the throttle body area. If it is set too low the IAC will not be able to raise the idle speed very far when cold. Conversely when the base idle is set too high the IAC won't be able to drop the engine back to the correct idle speed on a hot engine.

  6. #6
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    258
    bee utey, I have not touched the idle speed but thanks for the tip I did take the throttle body apart to replace the o-ring since it was sucking in air there but I did not touch any of the adjustments... Might be worth a look when I get the IACV replaced.

    Speaking of which, I tried to take that thing apart and boy what was LR thinking. M4 bolts with locktite?! Ofcourse mine had been in there for 20 odd years and the first gently twist snapped the head clean of. If I leave al the nsfw words out, I did not say a lot...

    Anyway! After a couple of hours trying to get the snapped of bolt out, rethreading both holes, new bolts etc. I could finally get to work on the iacv. It was dirty so I took a wirebrush drillbit to it and... I unscrewed the centre pin. Ok I thought, good thing since I can get to cleaning the bloody thing a lot better. Got it nice and clean and smooth and removed some of the old hard grease and replaced with something fresh. I got the pin to move though with quite some resistance. Tried taking it apart again but to no avail. Pushing it further in was really hard too and since I did not want to break the bloody thing I just tested it out on the car. The idle speed was up instantly to almost 2krpm. I gave the computer and IACV some time to settle down but after a few minutes I could see the computer (faultmate) reduce the amount of steps to about 120 but nowhere near the 20 I've seen here and there. I doubted the IACV was doing it's job so I took it out once again and tried more force to get the pin to move. Something said snap and after that there as movement in the pin though I doubt it is still functioning as intended

    Seeing as a replacement is around $25 down here I simply ordered a new one and will pick this back up once that comes in.

    Cheers,
    -P

  7. #7
    TheTree is offline ChatterBox Silver Subscriber
    Join Date
    Feb 2013
    Location
    Gosford, NSW, Australia
    Posts
    2,510
    Hi mate

    Sadly I think your IVAC is toast, it says in RAVE not to push or pull the center shaft while cleaning it

    Steve
    MY96 4.6 HSE P38. Niagara Grey; "The Phoenix"
    MY99 4.6 HSE P38. LPG, Blenheim Sliver; "Voldemort" burnt to a cinder
    MY79 RR Classic, Gone, MY57 Series 1 SWB, Long gone
    P38 write ups and info on my website http://p38.hts.com.au/

  8. #8
    Join Date
    Jan 2016
    Location
    Netherlands
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    258
    So I replaced the IACV. It turns out that it was an aftermarket unit that is also used on a jeep grand cherokee according to the seller. This means that the plug is on a bit of a weird angle for our application and the wiring harness is barely long enough. I am considering replacing it with one that has the plug in the right position but for now at least my car idles below 2krpm

    This is where the good news stops though. I could not get the car to idle normally whatever I tried and how much time I have the engine to heat up, it was stuck at around 2krpm. In a last ditch attempt (seeing as the old one was most likely broken to begin with) I reset all the adaptive values and et presto, the idle rpm dropped to 750-ish immediatly. hurray! or so I thought.

    The engine idles a bit rough but it always has, in my opinion this is due to the piper 285 cam. However when I try to move the car the idle is disastrously low, stalling the vehicle. Most suggestions around on the web state that it is the IACV but I just replaced it

    This is what happens:

    Car from park in drive, idle picks up well with the added load. I can set of without problem and drive around without problem as long as I do not stop. Once I come to a stop the idle drops to low 200's. The only reason the engine stays on is that a V8 has more power strokes than a four banger if I wait for say 10 seconds the idle slowly recuperates and I can set of normally. If, on the other hand, I need to drive in stop and go traffic the engine will stall.

    When reversing, I put the car from park in reverse and the idle picks up well again. Releasing my foot from the brake the car will move backwards but by the time the car reaches the speed that is equivalent to idleing backwards the idle drops like a brick to low 200's and often even lower and stalls.

    By that same token; making a 3-point turn is impossible; switching quickly between gears (through neutral) does give a fairly normal idle of 500rpm during the short period of time the car is in neutral but when in gear it will drop to the low 200's again and releasing the brake to actually try and move will stall the engine.

    I have been playing this game for an hour or so yesterday, intermixed with normal driving and the adaptive value learning system has managed to get the rpm at least stable enough as to not stall the engine every time I come to a stop, but it still drops to far for my taste.

    Finally I tried a "cold" start this morning, I left the car out and with an outside temp of 15c we can argue about the "cold" part there but hey The car started fairly normaly but it did not start with a high idle, the kind that keithy described but I hesitated a bit around 800rpm before settling on 900-ish and remaining there for the few minutes I let it run. I had to get to work so I did not connect the faultmate or drive around this time, I was just curious to see what would happen.

    All in all this is "workable" but not really what I was looking for. The rave manual (and I have not read every single page but searched on IACV) is not really helpful here, perhaps there is some adjustment procedure I do not know about...

    What I have done recently: fixed an air leak, replaced the MAF sensor, fix the PCV and replaced the IACV.

    Anyone have any ideas?

    Thanks!
    -P

  9. #9
    Join Date
    Feb 2010
    Location
    Townsville, QLD
    Posts
    2,523
    You mention youíve fixed an air leak. To me it sounds like a massive vacuum leak. Perhaps as far as a stuffed intake manifold gasket.

    If you squirt water (gently) over the intake manifold while itís idling, does it change how the engine runs?

    Cheers
    Keithy

    Green 2000 P38 Range Rover HSE - Gone
    Blue 1999 P38 Range Rover HSE - Gone

    Silver 2002 P38 Range Rover HSE - Sequential LPG, BCDC Charger, TPMS, Rear Locker, Wheel Carrier, Bullbar & Spotlights, General Grabber AT2's, Too Much to Mention!

  10. #10
    Join Date
    Aug 2018
    Location
    Brisbane
    Posts
    36
    what maf sensor did you get and why did you replace it and not just clean it? mine is still running the original LUCAS one and it's fine 320k later, all I do is CRC clean once in a while, with the GEMS I would buy the exact OEM replacement (probably Bosch) or else you'll get nowhere with cheap YumCha ones

    the biggest difference in idle and off idle pickup I've noticed was with new plugs

    I find that most remanufactured parts these days are absolute crap, special MAF/MAP sensors and finding an OEM replacement is hard, I would take the multimeter out and check the new sensor works as expected

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