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Thread: So what am I missing, still have rough idle when cold.

  1. #1
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    So what am I missing, still have rough idle when cold.

    Pulled some codes a while ago (cant remember what they were) search revealed CCV problems. Replaced with a new Meyle unit and new gasket. While replacing it, the sucking jet pump (brake booster vacuum valve) broke in half. Replaced with OEM unit, it came with the two short hoses.

    Few days later had SES light (P0443 code) search revealed fuel tank breather valve and/or gas cap. Replaced valve with Genuine BMW unit and OE gas cap. Still running rough but no codes.

    Suspecting a vacuum leak I sprayed all hoses with MAF cleaner while cold and hot but no change in idle.

    It purrs when warm but chugs when cold, maybe a little better since the repairs but no codes over the last three days and it has been cold out.

    Any suggestions?

  2. #2
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    Are you able to see fuel mixture adaptations with your scanner?

  3. #3
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    Quote Originally Posted by MikeEdmonton View Post
    Are you able to see fuel mixture adaptations with your scanner?
    I have the Creator C501. It appears to have a few options I have not played with yet and sadly I probably don't know what I would be interpreting?

  4. #4
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    http://www.easterncatalytic.com/educ...agnostic-tool/

    The first link from Google about fuel trims. BMW uses terms additive and multiplicative. If it runs poorly mostly at idle, you should check additive numbers first. If you have a high positive number, DME is trying to add fuel because the mixture is too lean, if number is negative - than the mixture is too rich. In case of lean mixture it would be 10 times easier to smoke test intake system instead of spraying MAF cleaner.

  5. #5
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    Quote Originally Posted by MikeEdmonton View Post
    http://www.easterncatalytic.com/educ...agnostic-tool/

    The first link from Google about fuel trims. BMW uses terms additive and multiplicative. If it runs poorly mostly at idle, you should check additive numbers first. If you have a high positive number, DME is trying to add fuel because the mixture is too lean, if number is negative - than the mixture is too rich. In case of lean mixture it would be 10 times easier to smoke test intake system instead of spraying MAF cleaner.
    That is some great info. I will look at the scanner and see what data I can retrieve. Thank you.

  6. #6
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    Quote Originally Posted by MikeEdmonton View Post
    http://www.easterncatalytic.com/educ...agnostic-tool/

    The first link from Google about fuel trims. BMW uses terms additive and multiplicative. If it runs poorly mostly at idle, you should check additive numbers first. If you have a high positive number, DME is trying to add fuel because the mixture is too lean, if number is negative - than the mixture is too rich. In case of lean mixture it would be 10 times easier to smoke test intake system instead of spraying MAF cleaner.
    So what I'm looking for is comparing the percentage of LT and ST% of FT at idle compared to higher RPM. If LT and ST% decrease then it points to vacuum leak? It appears I would then need to run the smoke test since my MAF cleaner approach didn't reveal anything.

  7. #7
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    If trims decrease at higher RPM comparing to idle and go to more positive numbers at idle than there is a lean mixture. It can be caused by many things but the most common is a vacuum leak. Smoke test is a much better way to find them than spraying flammable liquids around the engine.

  8. #8
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    a constant vac leak becomes a lower proportion of the total air taken in as rpm is increased. a larger quantity of air is drawn thru the MAF as the throttle body plate is opened, but the leak remains a fairly constant amount of air getting in to the engine. fairly, as negative pressure in the intake system increases and may effect the draw thru rate. agree completely with the above suggestion to do a smoke test. googling for it will show you many options for homemade smoke testers, or most shops could do it for you at a reasonable price.

  9. #9
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    well SES light came on (P2187 and P2189). Still trying to find the leak so I sprayed the throttle body flange and gasket a bit heavier and I was able to get the RPM to rise. I ordered the new gaskets and flange and will replace over the weekend. I hope that is the cause but, I did find a smoke tester I can get access to as well.

  10. #10
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    well I replaced the throttle body flange and the three different gaskets from the manifold out. The old gaskets were very hard and brittle. They had to come out in pieces. I cleaned the TB, it was pretty dirty on the manifold side. The car was already warm so I reset the error codes and we shall see in the morning. I did find that the Creator C501 has ST and LT fuel trim measurements and graphs. At idle the ST was at -10.2 % but the engine was warm and idling at 750 rpm. Ill check in the a.m. when cold.

  11. #11
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    So what am I missing, still have rough idle when cold.

    Common idle issue on e39 is also Fuel Purge control solenoid. It’s mounted on the drivers side front of the engine. They can throw their own code, but I’ve seen these type of symptoms from a failed Purge Contr. Solenoid without codes being present. A lot of times you can unplug it and tap it up against something solid and it’ll potentially free up enough to determine if it’s the issue.
    Of course I always check the larger rubber hoses as well and trace them all the way to their source with brake clean, such as spraying the end on the brake booster etc, it’s always the ends that like to split and leak.
    Lastly with the variations being related to temperatures, pull the coolant temp sensor and make sure it’s clean. There are 2 temp sensors, one for the gauge and one for the DME. The gauge could be accurate and still the other sensor might be acting up electrically or be dirty.

    Beyond those few things it’s hard to imagine anything that wouldn’t be a simple diagnosis. If you’ve confirmed no vac leaks and checked things like the TB, manifold, cleaned MAF, and the TPS is all good no leaks then it would be tune related in the STFT (fuel trims).
    Also remember if you had an issue, and fixed it already... the car may act up for a short period of time and get better the more you drive it. The trims will correct themselves intrinsically. Once you mess with something it could be, give the DME time and drive it more than usual, with a frequent pull over to shutdown and restart for cycling purposes. Best of luck these little issues suck I know


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  12. #12
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    Quote Originally Posted by 1gr8e39 View Post
    Common idle issue on e39 is also Fuel Purge control solenoid. It’s mounted on the drivers side front of the engine. They can throw their own code, but I’ve seen these type of symptoms from a failed Purge Contr. Solenoid without codes being present. A lot of times you can unplug it and tap it up against something solid and it’ll potentially free up enough to determine if it’s the issue.
    Of course I always check the larger rubber hoses as well and trace them all the way to their source with brake clean, such as spraying the end on the brake booster etc, it’s always the ends that like to split and leak.
    Lastly with the variations being related to temperatures, pull the coolant temp sensor and make sure it’s clean. There are 2 temp sensors, one for the gauge and one for the DME. The gauge could be accurate and still the other sensor might be acting up electrically or be dirty.



    Beyond those few things it’s hard to imagine anything that wouldn’t be a simple diagnosis. If you’ve confirmed no vac leaks and checked things like the TB, manifold, cleaned MAF, and the TPS is all good no leaks then it would be tune related in the STFT (fuel trims).
    Also remember if you had an issue, and fixed it already... the car may act up for a short period of time and get better the more you drive it. The trims will correct themselves intrinsically. Once you mess with something it could be, give the DME time and drive it more than usual, with a frequent pull over to shutdown and restart for cycling purposes. Best of luck these little issues suck I know


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    I replaced the solenoid a week ago. (Genuine BMW) Researching the codes lead me in that direction. It is funny how the car runs crappy for awhile right after I repair/replace something. I was assuming an adaptation. I have replaced everything you mentioned except the sensors. Ill see how it goes over the next few days. Thanks for the feedback and the support.

  13. #13
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    Disconnecting the battery will reset everything to the defaults, if you don't want to wait for things to re-adapt.

  14. #14
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    check the throttle body gaskets. Worked on mine.

  15. #15
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    Quote Originally Posted by upbeatgfx View Post
    check the throttle body gaskets. Worked on mine.
    That is what I did yesterday. I also replaced the flange and cleaned the TB. The car was still warm when I finished so I started it this morning. Usually its the first mile or so with all the stops that it runs rough or stalls. 38 degrees this morning and no idle issues or SES light, so far so good. I was going to wait a couple of days before I claimed its fixed.

  16. #16
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    You can hard reset DME by taking positive terminal off battery and then physically hold that positive cable against the negative battery terminal for 15-20 seconds. Leave the neg cable attached when you do so. Hopefully it is an adaptation. Have you stood back with a can of fiery aerosol and just kind of broadly sprayed down the majority of the engine bay? It’s a cheat to find out if there’s a vac leak you just were unable to pinpoint. Stand 4-5 feet away and just douse entire bay and listen for an idle change. If yes then start to isolate a general area, if no then you know theres no vac leak at all. Make sure motor isn’t fully warmed up and manifolds are moderately cool. Let us know


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  17. #17
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    well it appears to be fixed. After chasing codes, using search and direction from you fine people the cold idle issues are gone. Just to summarize:

    1) initial SES light after cold idle problems (can't recall error codes) replaced CCV, gasket and brake booster valve. Also replaced screws with SS hex head bolts and washers

    2) no improvement maybe worse now SES light P0441, P0443 code, replaced solenoid and gas cap

    3) still rough but maybe a little better after 2 days SES light and P2187, P2189. Replaced throttle body flange and the three gaskets. Replaced screws on flange with SS bolts and washers,
    Cleaned the throttle body with MAF cleaner and 90% isopropyl alcohol. Car has been idling smoothly for the last few days.


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