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Thread: High/surging idle

  1. #1
    Join Date
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    1988 e32 730i M30B30 MT

    High/surging idle

    Hi, I've got an 88 e32 730i manual.

    So I dropped the car off to get the tracking checked the other day, and it was fine, had run fine the two days beforehand too. Went to pick it up and it now has a high idle speed and surges up and down around 1500rpm.

    Garage chap says he had trouble starting it and told me to go away and Google the problem, so here I am.

    I've cleaned out the idle control valve, no change. Any ideas?

  2. #2
    Join Date
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    11/88 E32 750iL+98 E36M3
    surges up and down is usually an air leak in the intakes system, unmetered air is sucked and the MAF tries to adjust, check for cracks in intake rubber parts.
    Short summary on what will get your M30 to idle poorly:

    1) Ignition - plugs, distributor, wires, coil, alternator
    2) Vacuum leaks - oil pan, AFM leaks, intake manifold leaks
    3) Faulty valves - ICV, vapor release valve, fuel pressure regulator, sticky injectors
    4) Fuel pressure irregularities - FPR, failing pump, fuel line leaks, fuel filter
    5) Parasitic drag - water pump, alternator, compressor
    6) Engine block - valve clearance, worn lifters, uneven compression, oil pan leaks
    7) Electronics - temperature sensors, O2 sensor, ECU
    8) Exhaust - non-metered air entering before or around O2 sensor, any kind of crack or penetrating rust might cause sporadic idle problems

    also check the vacuum hoses http://www.nmia.com/~dgnrg/hose_map.jpg
    https://www.bimmerforums.com/forum/s...se-connections

    My Cars e32 730i
    pls add more details to your profile, something like xx/88 E32 730i M30B30 MT RHD
    helps us to help you.
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
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    Cheers, Shogun. Have found the vacuum hose that runs from beneath idle control is in two parts, likely culprit? Garage chap may be off the hook.

    Oh, excellent diagram by the way.
    Last edited by MasterE; 03-12-2019 at 04:05 PM.

  4. #4
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    Hi, I'm assuming that I may need to replace all the vacuum lines if one has gone, wondering how much hose and what size I should pick up to replace the lot? Will probably get done when the weather improves.

  5. #5
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    1990 735I (E32) M30
    Quote Originally Posted by MasterE View Post
    Hi, I'm assuming that I may need to replace all the vacuum lines if one has gone, wondering how much hose and what size I should pick up to replace the lot? Will probably get done when the weather improves.
    The hose from the bottom of your idle control valve that was broken is a specific part. It goes from the ICV to the back of the intake manifold. Looks like this and is available.



    The other larger hose that goes to the rear of the intake manifold comes from the purge valve. You'll know the purge valve by following the line from the charcoal canister the the motor. That little hose looks like this and is also available.



    There are only two vacuum lines on the M30. One comes off the top of the fuel regulator and the other comes out of the plastic attached to the boot. Both of these go to the bottom of the intake manifold. Any old vacuum line will do.


    See here on the other side of the boot where your idle control valve is, and the top of the fuel regulator. Only two vacuum hoses on M30. Purge valve in picture to right of the oil dipstick. See the hose coming off of it.

    Last edited by CroughtonE32; 03-13-2019 at 09:08 PM.
    1990 735I (Auto) E32 Feb 1990 to Present
    1996 Z3 Roadster (5 Speed) E36/7 Jan 1999 to Dec 1999
    1983 733I (5 Speed) E23 April 1983 to Feb 1990
    https://www.youtube.com/watch?v=2d4tHoHGaJo
    https://1drv.ms/v/s!Av20xCMMocSsyEpl...h_oOk?e=ekIcAT







  6. #6
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    11/87 735i & 735il P/C
    RealOEM and FCPEuro - that's my 2 cents. With that combo I replaced all the vacuum & intake hoses on my 735, minus the fuel regulator hose, which I found on Amazon (from memory I think any old high temp 3mm ID silicone hose will work for that one)
    Last edited by CamE32; 03-13-2019 at 07:11 PM.
    1983 4-spd Mercedes 240d w/403k - Sold!

    11/87 E32 735iA w/45k - Daily Driver (finally!)

    04/88 E32 735iL - Parts Car

  7. #7
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    Just checked Real OEM. Typed in your car. 88 730I Euro, RHD. Just to make sure the hoses were the same as mine. Here are the three part numbers if you want OEM hoses and vacuum lines.

    13411710793 Part number for ICV hose

    13311288284 Part number for hose from purge valve to back of intake manifold

    11727545323 Part number for OEM vacuum hosing. You can use this for both vacuum lines. Although the factory vacuum line from the boot was white, this black vacuum line is good for both. Hope this helps you out on the other side of the pond.

    Last edited by CroughtonE32; 03-13-2019 at 09:25 PM.
    1990 735I (Auto) E32 Feb 1990 to Present
    1996 Z3 Roadster (5 Speed) E36/7 Jan 1999 to Dec 1999
    1983 733I (5 Speed) E23 April 1983 to Feb 1990
    https://www.youtube.com/watch?v=2d4tHoHGaJo
    https://1drv.ms/v/s!Av20xCMMocSsyEpl...h_oOk?e=ekIcAT







  8. #8
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    Hi guys, cheers for your help, plan to replace the obvious failed hoses first, awaiting delivery. Not been driving the car, only turning it over to test it as I've been pinching/taping up hoses etc, which has made no noticeable change. Wondering if it's okay to run the car out with its current problem or if maybe I even should take it for short runs?

    Also, whilst nosing about, wondering how I tell if the engine has L-tronic or Motronic? Have read that the 3.0 had L-tronic and they only started putting Motronic on the 3.5. Not sure what difference that makes to me, but I understand idle speed can be manually adjusted on L-tronic.

    Cheers in advance, just sitting here waiting for the latest storm to move on.

  9. #9
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    All E32 have Motronic, your 1988 730 M30B30 may have a M1.1, can be replaced without problem by a M1.3, if required https://en.wikipedia.org/wiki/Motronic
    https://www.bimmerforums.com/forum/s...ic-1-1-1-3-BMW

    Make a smoke test for unmetered air leaks , DIY smoke tester samples
    https://www.youtube.com/watch?v=GOhl4r0GSiE
    https://www.youtube.com/watch?v=L9CDZ9lu6Rs
    https://www.youtube.com/watch?v=Np_duzsaZxI
    Last edited by shogun; 03-16-2019 at 10:18 AM.
    Shogun tricks and tips for the E32 series are HERE!

  10. #10
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    Time for an update. Disconnecting the volume air flow sensor drops the idle speed to 800, testing the resistance across the contacts and there is a steady increase to about 2kohms as I open the vane before it begins to drop again as I continue to open it further. Currently have it off the car and letting some cleaner soak in, not convinced that will help yet.

  11. #11
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    Check your oil filler cap or dip stick, BMW's don't like it if they are not on properly.

  12. #12
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    Hey guys, right, swapped the air flow for another, no change, tested voltage and resistance values as per Bentley on air flow, throttle, idle control and temperature sensors and seem okay, checked continuity to the ecu and checks out okay. Any ideas?

  13. #13
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    Changed idle control valve, no change, changed ecu, big change, idling smoothly at 800, but... Old ecu would not turn on the check engine light, not even on start up test, no output to it at all, new ecu idles engine nicely at 800 but the check engine light is flickering. Not flashing, not solid, flickering rapidly like a dodgy connection. My car doesn't have a cat, I thought the light was for emission issues and not having a cat or sensor it did nothing, so wondering what's confusing this one. Stomp test brings up 1444, no codes. Hmm...

  14. #14
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    Your U.K. car should not have a check engine light at all. I am not familiar with check engine light as this is something especially for the US. Some people in Europe modify their cars to check engine light function and as far as I remember the usually install a wire between the DME and the cluster and install a bulb in the cluster (EURO cars do not have a bulb installed in the cluster for that). So the easiest is you just remove the bulb from the cluster.
    Here is an old thread from the German forum, he also installed a check engine light on his E32, but the problem was, that the light was always on then , he installed a switch to switch it off for normal driving and switched it on for testing only
    http://www.7-forum.com/forum/showthr...ght=stomp+test
    he comments: he installed a grey wire line from the DME to X16 pin 23, from X16 to X502 pin 3 the line was existing.

    X16 and X502 are plugs in the rear of the cluster http://www.e32-schrauber.de/bmw/s-stecker-kombi.htm

    4 plugs in total, X17, X16, X271, X502
    Shogun tricks and tips for the E32 series are HERE!

  15. #15
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    Cheers Shogun, I will not worry too much about the light then, may fit a switch for the stomp test, a little odd that this ecu picks up on the light but the other one didn't, the way that it is not a solid or a blinking light does make it look like it may be a poor contact issue anyway. Will keep an eye on things,engine idling correctly without surging is a vast improvement so far.

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