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Idle problems revisited

Discussion in 'E30 (1984-1993)' started by az3579, Oct 26, 2008.

    • Member

    az3579

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    I've decided to take another crack at my oh-so-infamous E30 idle problems.

    A recap of the situation:
    When I got the car two years ago, it idled fine, with the stock ICV in place, plugged in.
    About 3/4 of a year after that, during the summer, my idle surged beyond belief into the 3000's. Unlike most peoples' idle problems, however, my idle stayed there; 3500RPM steady. This made it driving in town almost impossible and pretty much reduced the lifespan of my clutch.

    My brother came up with an ingenious solution. He mounted a plumbing valve inline to the ICV and regulated the idle speed with that. At the moment, the valve is set to a particular position and regulates the idle to 1000RPM.

    Why 1000? When cold, the engine will rev lower than that, say 650-700RPM. A strange problem has reared its ugly head when the idle would drop (when cold) a few hundred RPM and the engine would make a strange knocking noise. If I raised the RPM's to prevent it from doing that, it would still drop and make that knocking sound, even if it isn't near stalling speed. So, if I start the car (with the valve set to 750-800RPM when warm), it will stall almost immediately if I don't keep the revs up until the engine warms up. I'm not going to sit there and keep revs up while waiting for it to warm up. This knocking thing is a completely different issue and is irrelevant to my idle problems, which existed before the knocking started happening.

    So why bother with the idle problem if it's "sorted" with the valve set to 1000RPM?
    Well, I have to submit the car through emissions by March and the last time it was inspected, it was before my idle problem occurred in the first place. I'm afraid it won't pass emissions. Currently it's running rich, I'm guessing due to the high idle speed set by the plumbing valve. Also, winter is coming, and it will be harder to keep the revs up when cold starting, especially when I'm running to work and risk being late if I wait for it to warm up, so I have to drive in traffic, keeping the revs up 'till I reach the freeway, which is a major pain and stall multiple times in the process.



    Now, diagnostic steps taken:

    I replaced the stock valve that was in the car when purchased with a valve bought on eBay. It was a valve that was 20 years old, but brand new (never used). I figured for $20 or so, it couldn't hurt to give it a try. I put that bad boy in there and was fine for a few days. Then, the idle from hell returned, revving at an optimistic 3500RPM. I also tried another used valve bought from a parts store and that did it as well.

    Some say it's a vacuum leak, but if that is the case, then why doesn't the idle surge when the plumbing valve is in place? If it was a vacuum leak, then wouldn't it happen even with the plumbing valve in and the ICV disconnected? Currently I run with the ICV disconnected and the PV in place.

    With the PV set to fully open and the ICV in place, the idle from hell becomes apparent. When it doesn't idle 3500, it surges between idle and 1300 RPM, which is still unacceptable.



    So, my main question is; could it still be a vacuum leak if it doesn't affect idle with the PV in place and ICV disconnected?
    • Member

    MGarrison

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    Wish I was more of a armchair diagnostician for you - I don't know if this will help but - I had an idle surge that wouldn't go away - I replaced everything related to it, no go. Finally, last thing I did, was swap ECU's - the idle circuit in the original ECU was bad; different ECU and idled just fine. If you can get your hands on a known-good spare, you might try plugging it in just to give it a shot. I can't speak for all the differences between eta and motronic - if 325e idling is in no way tied into the ecu, that's obviously not going to make any difference. You don't have to remove the original ecu, I think you can just disconnect the harness connector to plug another in.
    • Member

    az3579

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    I don't have access to another ECU. I'd be damned to find another E30 anywhere near here in the junk yards, or even on the street for that matter. :(


    Unless you have a spare you could ship just for testing?
    • Member

    MGarrison

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    Sorry, I don't - dang, too bad you don't have some sort of long-time BMW-only indy shop around w/ a pack-rat amiable owner. ECU's can be had off ebay, but if that wasn't the problem, you're stuck w/ a spare, or you have to re-sell it. ECU's w/ the same part number are interchangeable, you'd have to look at yours to get the part number on it and see if you could find a twin. Given how much one is to replace from BMW, it's not a bad idea to have a spare as a just-in-case, if you're keeping the car for the long haul.

    http://search.ebay.com/BMW-E30-325e...Q2d1QQssPageNameZRC0022QQ_trksidZp1638Q2em120

    I'll let ya know if I think of anything else to diagnose, idle-wise -
    • Member
    • Technical Service Advisor

    mooseheadm5

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    The ECU does not control idle in this car. It is controlled by an aux idle control unit (the Green box.) This is what causes your problems and the only solution is to replace the green box and the ICV because a fault in one can take out the other. My old boss used to just take a plastic plug and drill a 1/8" hole in it and insert it into the idle air line. Works quite a treat. I'll get back with more in a bit. Gotta work.
    • Member

    az3579

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    This green box is inside the ECU casing, correct? I heard of something like that near where the ECU is, but I haven't ever paid attention to anything other than the performance chip I swapped in when I took out the ECU.

    I'll look again and see if I could find a green box that you mention.
    • Member
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    mooseheadm5

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    It lives above the ECU in your glove box, not inside the ECU. It says VDO on it somewhere (it may actually be blue, but 99.9% are green.) Pretty sure it is not your ECU causing it. I have 3 or 4 if you need to test, though. Don't think I have any green boxes, but I'll check. Also, make sure your AFM door isn't binding, but it sounds like a green box problem to me. There is a screw on the ICV, should be on the outside. Shut it all the way to take most of the opening travel out of the ICV. See how much that helps.
    • Member

    az3579

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    Ya know, I have a can of CRC AFM spray that I've had for well over half a year and never used. But come to think of it, if the door in the AFM was binding, that would affect my idle even with the plumbing valve controlling idle, wouldn't it?


    I'll definitely look for that green box thing. It can't be too expensive from the stealer for a new one.
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    • Technical Service Advisor

    mooseheadm5

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    $411.80 by realoem.com
    • Member

    az3579

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    ARE YOU F*CKING KIDDING ME?


    For what, a box the size of a USB hub, maybe smaller??? Or is it a more complicated part and I'm not fully appreciating the extent of this device's capabilities?

    Doing a search for it on eBay yielded no results. What is going on with this? Isn't this a common failure item?
    • Member
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    mooseheadm5

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    Well, it is an antiquated signal processor that only fits your car. What did you expect. Yes it is a common failure item, which is why you won't see it on ebay. Nobody will sell them if they need them and many people that junk the cars don't even know about it. See earlier post about restrictor hole and shutting screw on ICV. Enjoy :)
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    az3579

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    Ah HA! I just found like 3 or 4 of them on eBay, I was just searching under the wrong terms. I'm about to buy an idle control valve AND idle control module together for about $46 after shipping, pending a question to the seller about whether they've actually been tested. If they have and they work, then I'm going to pull the trigger.

    I don't know what else it could possible be if it's not a combination of the valve/ICM. If it was anything else, then my idle would be a problem even with my custom solution in place, so let's hope this fixes it.
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    granthr

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    Botond:

    I had idle issues on my 318i and it has the same set up as your eta, only it uses a different idle control module from your car. However, I was chasing down this fluctuating idle for a while and keep coming up empty handed. I tried different idle control valves and module, replaced vacume hoses, to no avail. Finally I took it to the dealer and they fixed it right proper in an afternoon! It turned out that my Throttle Position Switch was bad. This switch is on the throttle body. So if this new valve and module don't fix your problem, I think you should take it to an independant BMW mechanic or dealer to have them diagnose it. It will be money well spent if they can fix it. Good luck.

    GR
    • Member

    az3579

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    My problem isn't a fluctuating idle though, it's a constant high RPM idle. Also, if this switch was bad, then what other systems would it possibly affect and why doesn't it affect other systems if it's bad? Those are the questions that are making me lean towards ICV+ICM.


    I bought it a week ago but still hasn't arrived. I reeeeeeally don't like USPS - they're dog slow and completely unreliable. :mad:




    I really hope this fixes the problem because the hose that had to be "modified" to put in the plumbing valve as a replacement comes right off if you touch it, so if I hit a big bump, off it comes and I will stall. I need to order a new hose and I can't do that 'till I fix my idle.



    Wish me luck...
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    mooseheadm5

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    The M10 318i TPS sensor is more prone to this problem than the M20. If you want, it is easy to test, though, as it is just an idle switch and a full throttle switch.
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    az3579

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    Umm...


    Since I replaced the Idle Control Module (thanks once again for those pinouts!), my car idles normally, but only after a few minutes after starting up. It not idling properly at startup is the reason I replaced it, so I wouldn't have to hold the revs up until the darned thing warmed up...

    Now I start it and it idles OK, but the second I start moving and come to a stop, the idle drops too much, and it bounces the idle up in an attempt to keep it from stalling, but the revs drop faster than it expects and it falls to about 300rpm, at which point it bounces the revs up again, and it falls too low and stalls. This is absolutely ridiculous!

    Why could this be? Why can't the damned thing just WORK???



    It works just fine after the engine has warmed up, perhaps after the thermostat does something (what does it do, open up or close? ) and the car doesn't stall at all when coming out of gear after this time.
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    mooseheadm5

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    First:
    Has anyone fiddled with the throttle plate to close it off to adjust for the high idle? If so, it needs to be adjusted back to spec. This is a common band-aid to cover the high idle that signals the onset of idle control system failure. The base throttle setting is important, because the ICV can only open so far and is only there to let more air in after the base throttle opening is set properly.
    Second, does the 32 degree switch work?
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    mooseheadm5

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    BTW, the 32 degree switch is located on the firewall on the pass. side. The blue/green wire (pin 10) on the green box should get 12V with the key in run or start and ambient (underhood) temp below 32.

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