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Thread: Rough idle

  1. #1

    Rough idle

    After a short trip to the store, i noticed even with the car warm. When i started it up and idled in the parking lot for a minutes the idle got rough. Almost sounded like i had internal parts going out. I freaked out and shut the car off... I check oil, good. And no odd signs of something catastrophic. I start the car back up and it sounds fine.. Few seconds of idle the car gets rough again... but seems to adjust it self as the rpms went from 600 to maybe 800 and smoothed out... no more rough idle, it doesn't seem to last longer than say 15 seconds or so before it adjusted itself. Sounds like the engine is perfect. There seems to be a little hesitation while driving through the rpms as well... its not "perfectly smooth". With normal driving too.

    Now I know the fuel filter is original and i have one coming in tomorrow to change it along with new vanos seals... But besides that, does it sound like the DISA causing the issue? Should that be my next place of inspection if these few fixes don't work?

  2. #2
    Join Date
    Dec 2012
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    Salt Lake City, UT
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    Any codes?
    In the market for an E90 M3

  3. #3
    Join Date
    Jan 1970
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    Could be running rich/lean. Could have an intake boot crack/tear. ICV could be dirty. Would be nice if you could pull a code.

    Even if no SES light is present you may have a code stored.
    Call Me Dane l 2/2004 330i ZHP l 18x8 ET45 BBS CK's wrapped with Michelin Pilot Sport AS3+ @ 245-40-18 l KW V1 Coilovers in front l KW V1 springs w/ Bilstein B8 dampeners in rear l BMW Performance Rotors l UUC StrutBarbarian l Racing Dynamics Rear Strut Bar l Jim Conforti Shark Injector l Light Birch Interior Trim l Bimmian Celly Mount l M3 Trunk Mat l l e90 Performance E-Brake & Shift Knob l M3 Tri-Stitched Boots l AL Headlight Retrofit with ZKW Lenses l CobyWheel Wrap w/M3 Stitching l LCM sw 4.5 triple blink and rear fogs l Maple Interior Trim

  4. #4
    First chance i get Ill check for codes. No lights are being thrown.

  5. #5
    Join Date
    Oct 2011
    Location
    Silicon Valley
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    1,630
    I have a similar problem, though can't say if it's the same issue. Sometimes on hot start, if I leave it to idle in neutral with clutch engaged, it does the rough running thing for 15-20 seconds. If I rev the engine, it goes away. If I push in the clutch pedal, it goes away. If I start it cold or drive off immediately, it doesn't happen. Once or twice it threw a CEL but usually there is no CEL.

    My intake boots are fairly new. Upgrading DISA with GAS kit did not help (and GAS guy told me it probably wouldn't help before I bought their kit). One indie heard it happen in front of his shop and suggested flywheel or driveline thing, since it stops if I press in the clutch. I've got 172,000 miles on original DMF (2nd clutch), maybe its damping mechanism is failing?

    Haven't cleaned the ICV in 2.5 years and never cleaned the throttle body... those are possible issues.

  6. #6
    Join Date
    May 2012
    Location
    Atlanta, Georgia
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    It could be all sorts of things. As Dane mentioned, it could be an intermittent vacuum leak. Without a code, it's a lot harder to narrow it down. In these sorts of situations, I just run INPA and check all of the modules(specifically the DME in your case) and it helps me narrow down the possibilities. If you have a way to measure coil resistance and fuel trims, go that route. Otherwise there is always the old fashion way of diagnosing things.


    Start by disconnecting a coil pack one by one during the rough idle and see if it changes. If it doesn't then you know if you have an ignition issue.

    Disconnect the harness from the DISA valve and see if anything changes there (also a good time to see if your DISA valve is making any noise). If so, I recommend rebuilding it with the GAS kit. It's top notch.

    If all goes well there, move the intake boots around and see if you can't notice any difference there.

    Disconnect the MAF and see if anything changes.

  7. #7
    Also the rough idle isn't consistent. As in it will do it then stop... Doesn't consistently idle roughly... Also, as you mentioned try these techniques with the car running? I guess it would work only during the rough idle it self? Im about to get a scan in about an hour. Advanced does it free and its about 10 minutes from me. Looks like its time to order the actron cp9575 tonight.

  8. #8
    Join Date
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    I don't think the CP9575 scanner will get all the BMW specific codes, but it will pull all general OBD-II codes and let you monitor some real-time data, including live O2 sensor data, plus of course turn off the CEL. Even if I don't rev engine, drive off, or push in clutch, my rough idle stops after a while. I did replace all my plugs and coils about 18 months ago and my VANOS seals 2 years ago but that didn't solve this problem.

    Besides possibly being the dual-mass flywheel, sometimes I wonder if it's my CCV, which--if original--has 10 years and 172,000 miles on it.

  9. #9
    The guy at advance couldn't get my car to pull up on the scanner. I believe he was using the cp9580... Is this right or is that guy just not capable of using it correctly?

    Also, just now my drive to advance, typical small town driving, i had a little rough idle when i first started up, no where near as rough as before. I noticed the pressing of the clutch and turning the a/c on and off changed the roughness... A/c off it was more rough, a/c on it smoothed out... So something to do with the load at idle...this was the beginning of the trip. When i got back home, i idled for about a minute doing the same stuff the symptoms lessened so much that they barely showed. As in seems like nothing is wrong at all. So my problem doesn't seem major but is definitely showing signs that something is starting to go out. If my fuel filter is original at 105k miles i'm assuming the fuel pressure isnt consistent when im at idle the load type on the engine is what caused to be rough or smooth.

  10. #10
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