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Thread: Wandering/high idle. I知 stumped.

  1. #1
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    Wandering/high idle. I知 stumped.

    I bought a 97 M3 a couple months ago. I致e been throwing parts at it ever since, and nothing has helped. Sometimes it idles really high, sometimes it jumps around, other times it repeatedly climbs and falls.
    Here痴 what痴 probably not the problem, because I checked and/or replaced them already...
    MAF
    FPR
    ICV
    CCV
    TPS
    O2 sensors
    Any kind of vacuum leak, I知 99% sure.
    Compression loss

    Edit: Add EGR, SAP. Forgot to mention as they have been removed.

    I知 not getting any useful error codes. What am I missing? Could it be a timing issue? VANOS? I have INPA but I have no idea what to look for at this point.
    Attached Images Attached Images
    Last edited by dtownmikebrown; 12-14-2018 at 11:09 PM.

  2. #2
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    I am not well versed in reading inpa. But it seems to me that your car should not be under load while idling. Check your throttle cable adjustment. But honestly it sounds like a vacuum leak and my car did the exact same thing when it had a large vacuum leak.

    Edit: I don't see EGR mentioned anywhere on your list of parts youve checked. I'd inspect that as well

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    Last edited by XnWarden; 12-14-2018 at 10:12 PM.

  3. #3
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    Yeah when you took those screen shots the rpms were high. You really need to smoke test it to get all the vacuum leaks.
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  4. #4
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    I guess I’ll do a smoke test to rule it out, but I really don’t think it’s a vacuum leak. I checked the vacuum hoses associated with all the things I mentioned above. I also plugged the EVAP and brake booster lines to rule them out. Also replaced the gasket for the throttle body and deleted the ASC and accordion intake boot with a bimmerworld intake boot. Everything connected to the intake manifold is air tight.

    i checked the throttle cable. Feels like the right amount of slack. Butterfly valve seems like it closes all the way shut, but the stop makes contact with the set screw. Does that need to be adjusted?

  5. #5
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    Looking at all the parts you checked/replaced, and if there really is no vacuum leak, one more option could be that your DME is defective. Such that it's unable to drive the ICV properly. But I would first do the smoke test to be really sure.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  6. #6
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    I like the DME theory. It might be defective, but I'm able to get live values from all the sensors in INPA, so maybe it's a tuning issue. It's also worth mentioning that the car has been messed with by at least a few previous owners. For example, when I got it, it had OBD-I headers with the o2 sensors plugged into the pyrometer ports on cylinders 3 and 4. I figured if it made really good compression and shifted smoothly into all 5 gears, everything else could be sorted out easily enough. I found SO MANY things on this car that were obviously wrong, thinking that I had finally found the culprit, and then it would run just as bad or worse. Unfortunately, I have no record of any work that had been done prior to last owner.

    Here's what I do know for sure: The DME cover has been opened at least once, everything up to the throttle body has been removed at least once, and the the wires coming from the MAF sensor connection are spliced. Maybe it's been tuned for an M50 intake and a different MAF sensor. Maybe other things, too. Odd that I haven't seen any error codes related to the SAP or EGR even though they're long gone. I'll smoke out any remaining vacuum leaks and report back.

  7. #7
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    Disconnect the brake booster vacuum hose and hook up a vacuum gauge to the manifold and see what the measured vacuum is. It should be around 15-20 in/Hg iirc

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  8. #8
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    I did some research on reading inpa values. The reported air consumption is too high. Idle speed air consumption should be around 15kg/h and yours is double that

    Shoot a pm to 328 power 04
    He can point you in the right direction

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    Last edited by XnWarden; 12-16-2018 at 10:31 AM.

  9. #9
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    Quote Originally Posted by XnWarden View Post
    I did some research on reading inpa values. The reported air consumption is too high. Idle speed air consumption should be around 15kg/h and yours is double that
    Except, the screenshot wasn't at idle, but at 1700 rpm.. So probably a normal reading..

    Perhaps Mike can redo the INPA readout, but now at a stable (if possible) 700rpm idle. Then we can compare values properly.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  10. #10
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    Quote Originally Posted by ed323i View Post
    Except, the screenshot wasn't at idle, but at 1700 rpm.. So probably a normal reading..

    Perhaps Mike can redo the INPA readout, but now at a stable (if possible) 700rpm idle. Then we can compare values properly.
    I believe he said his car idles at 1700 rpm which is why i initially suspected a misadjusted throttle plate or cable

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  11. #11
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    Quote Originally Posted by XnWarden View Post
    I believe he said his car idles at 1700 rpm which is why i initially suspected a misadjusted throttle plate or cable
    I can't get the idle to sit still long enough to get a good reading. It bounces around anywhere from 1500 to 2200 rpm. I have seen it settle down to the proper idle speed a few times, but then it stumbles again after a few seconds and jumps back up. The throttle stop is resting on the set screw, but maybe the screw is backed out too far. If I remember correctly, it's supposed to be backed out all the way and then tightened a quarter turn. I'll have to verify that and adjust accordingly.

    Here's an update: Over the weekend I drove the car out to a friend's shop to weld a crack in the exhaust midpipe. That quieted things down enough that I could hear a bad clanking sound coming from the engine bay. I pulled the codes again when I got back home and found error code '212 VANOS mechanical jamming'. I've never experienced VANOS rattle before, but it sounds a lot like what people have described. I ordered a refurbished actuator and a rattle repair kit along with all the seals and gaskets. It might not solve my idle issue, but I'm sure it's not helping anything either.

  12. #12
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    Perhaps, what you could try is take the ICV out of the equation, and then adjusting the throttle stop so it idles at say 900-1000 rpm warm and 700 rpm cold (if possible).
    I think you could do this by removing the hose at the rubber intake boot that connects to the ICV and use a large piece of duct tape to cover the opening of the hose (and wrap the sides of the tape down the hose), and then reinserting the hose into the rubber intake boot. I hope I explain it clear enough.. That way, no matter what the ICV does, there is no air going to the ICV, so nothing happens.

    Then, if the idle becomes stable, you might get a better idea wat what's going wrong, and you'll have a car that's better drive-able than now. Please note the compromise will be that it runs at too high rpm when warm, because you have to make sure it keeps running when it's cold, at say 700 or 750 rpm.. That same opening of the throttle body butterfly valve will correspond to say 1000 rpm once the engine is warmed up.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  13. #13
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    Quote Originally Posted by ed323i View Post
    I hope I explain it clear enough..
    This makes perfect sense and I will give it a try.

  14. #14
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    I rebuilt the vanos unit with new seals and a refurbished actuator. Power delivery in the lower rpm range is a lot better, but it didn't do anything to help my idle issue. I still had the feeling the throttle plate set screw had been messed with, so I tightened the set screw to open up the throttle a little bit more. That solved the issue where the car would bog down when taking my foot off the accelerator, but the idle issue hadn't improved.

    Then I did what ed323i recommended and blocked off the ICV outlet to the throttle boot. At operating temp it idled steady at 1200 rpm with very little variation on the INPA "roughness" screen. Then I unblocked the ICV hose and the idle jumped back up to 2500rpm and then started searching again. Now I notice that the idle is consistently inconsistent. It climbs up and falls at the same rate and RPM. So that's a step in the right direction, I guess. No new error codes now that the vanos has been fixed.

  15. #15
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    Great progress! Cool the Vanos now works fine.

    I think this probably narrows it down to a bad ICV (and it seems you already replaced it with a new or known-good one), bad wiring from DME to ICV (or perhaps DME relay to ICV), or some electronic components in the DME gone bad. If you're thinking of buying another DME, you can consider looking at the chipped DME link in my signature. EWS-delete is a free option, or you can just resync the DME to the EWS in your car with a simple program. It makes the 323i a lot faster, and you can really feel it (whereas for example with an M50 chip tune you really have to make an effort to feel the difference; 323i is very much down-tuned from factory).


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  16. #16
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    I swapped in the throttle body from a different car, started it up (with the ICV connected this time), and after a few minutes the idle settled right down into the ~700rpm range. I'm sure the ECU needs more time to adapt. I don't want to speak too soon, but I think I can consider this case closed.

  17. #17
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    Change it with the tps on the throttle or still have the original?
    Nobody would recertify these machines after somebody screwed with them without any visibility into what they did.

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  18. #18
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    Everyone is making this more difficult than it is. Make sure the ICV moves with 0 resistance and I mean 0. DO A VACUUM LEAK TEST!!!! This is the most important first step on any fueling or idling issue on an E36!!!! There are too many places that can leak to just "check hoses", the only proper way to test this is with a high dollar smoke machine (until someone figures out how to use a VAPE to make a low pressure smoke machine) Also disconnect the cruise control cable and make sure it wasn't causing an issue, mine was a little tight and was holding the throttle open a little. Any components that were replaced, if they are not OEM or from the original manufacturer then they are suspect.

    Don't replace the ECU, it's almost never the ECU.
    Last edited by somebody5788; 02-01-2019 at 09:59 AM.
    1997 328is - Megasquirt PNP, Holset HX35, Deka 80lb injectors, SPA T3, Precision PW39 WG, Synapse Synchronic BOV, DKM Organic Twin Disc Clutch, Innovate LC-2 W/B, Mishimoto Intercooler, Mishimoto Catch Can, Mishimoto Rad, Devils Own Meth, Porsche 911 calipers with E46 M3 rotors, Corsa Exhaust

  19. #19
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    I fired it up again this morning. It sounded/felt A LOT better after getting closer to operating temp. After the 45 minute drive to work the idle was very smooth and steady when I parked. I知 still planning on having the ECU reprogrammed to account for the deleted SAP/EGR/Evap/cats and overwrite whatever tuning for different hardware might still be on there.

    Quote Originally Posted by spyderg0d View Post
    Change it with the tps on the throttle or still have the original?
    I had already replaced the TPS on the old throttle body with a new one, so I transferred that one over to the replacement throttle body.


    Quote Originally Posted by somebody5788 View Post
    Everyone is making this more difficult than it is. Make sure the ICV moves with 0 resistance and I mean 0. DO A VACUUM LEAK TEST!!!! This is the most important first step on any fueling or idling issue on an E36!!!! There are too many places that can leak to just "check hoses", the only proper way to test this is with a high dollar smoke machine (until someone figures out how to use a VAPE to make a low pressure smoke machine)
    Like I said, I'm 99% sure there are no vacuum leaks. Ordinarily I would agree with you, but all the vacuum-operated emissions components have been removed and the associated connections capped off at the manifold, which narrows things down a lot. I replaced the valve cover gasket, oil filler cap, intake manifold gasket, TB gasket, injector o-rings, and torqued everything to spec. I replaced the grommets on the oil separator and ICV as well as the oil separator itself and both hoses. While I was at it, I replaced the o-rings that seal the dipstick/tube on both ends. The accordion intake boot was replaced with a silicone ASC delete boot between the TB and the MAF. I hooked up a T fitting between the brake booster and the intake manifold and verified it was pulling 20 in.Hg at idle. While I was replacing the fuel filter and FPR, I verified the vacuum hose was also intact and pulling 20 in.Hg at idle. If there's still a vacuum leak, I don't see where it could possibly be.

  20. #20
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    Mine pulls about 23inHg at idle at 210,000 miles.
    1997 328is - Megasquirt PNP, Holset HX35, Deka 80lb injectors, SPA T3, Precision PW39 WG, Synapse Synchronic BOV, DKM Organic Twin Disc Clutch, Innovate LC-2 W/B, Mishimoto Intercooler, Mishimoto Catch Can, Mishimoto Rad, Devils Own Meth, Porsche 911 calipers with E46 M3 rotors, Corsa Exhaust

  21. #21
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    Quote Originally Posted by somebody5788 View Post
    Mine pulls about 23inHg at idle at 210,000 miles.
    I haven’t tested it again since swapping throttle bodies. Now I’m curious.

  22. #22
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    Note that M52B25 and M52B28 will not pull exactly identical inHg values I think.
    M52B25 compression is 0.3 bar higher if I'm correct, at 10.5 bar (versus B28 10.2 bar; B20=11.0 bar) but the combustion volume is 300cc less.. Intake manifold, idle control valve and throttle body are identical though.. Not sure how that would work out in the actual inHg. I'd expect the 2.8 to "suck" more air through the same small throttle butterfly valve opening and hence create higher vacuum, but my physics/vacuum knowledge is just a bit too rusty to really say.. What do you think?
    Last edited by ed323i; 02-01-2019 at 08:42 PM.


    1997 E36 BMW 323i
    (European) 275k km (171k miles), with following small mods:

  23. #23
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    Just checked it again, still 20inHg. I keep forgetting to update my profile. I don’t have the 323is anymore. This is an S52B32US. Other than camshafts and displacement it’s pretty much the same as the M52B25 and the M52B28. Maybe the different cams account for the lower vacuum.

  24. #24
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    Quote Originally Posted by dtownmikebrown View Post
    Just checked it again, still 20inHg. I keep forgetting to update my profile. I don稚 have the 323is anymore. This is an S52B32US. Other than camshafts and displacement it痴 pretty much the same as the M52B25 and the M52B28. Maybe the different cams account for the lower vacuum.
    Long story short, I found out in a roundabout way that one of the previous owners blew the original S52B32US. It was replaced with either all or part of an M52B28. To find out, I pulled a spark plug and measured the stroke with a dowel. I measured 3.29" which is just about right for a 2.8L. Still not sure if the S52 cams were transferred over, so now I'm curious to find out.

    Over the weekend I was able to get ROMRaider running on my laptop. I found a stock 328is bin file, disabled the SAP, and did a quick re-flash. Now it's running almost perfectly, aside from the roughness screen on INPA fluctuating a bit more as it gets closer to the target 700rpm idle. I'll have to take some measurements on the camshafts.

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