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Thread: Rough Idle when Oil Filler Cap removed

  1. #1
    Join Date
    Mar 2004
    Location
    Warren, NJ
    Posts
    183
    My Cars
    2008 BMW 135i - Stage 1+

    Question Rough Idle when Oil Filler Cap removed

    I've been shopping for a 328. I've looked at a few that when I remove the Oil Filler cap, the idle drops and becomes somewhat rough. Put the cap back on and it idles like a kitten... When I drive the cars they feel fine.

    I am just curious as to why this would happen. I wouldn't purchase a car without a PPI, but I'd like to know if this is a real problem before I shell out the cash to have the car checked out.

    Any advice would be appreciated.

    Thanks
    Dave
    Last edited by DMan928; 03-28-2004 at 12:43 AM.

  2. #2
    Join Date
    May 2003
    Location
    By The Bay
    Posts
    1,041
    My Cars
    1995 325i, 2007 335i
    When you remove the oil cap the pressure drops and the engine will sputter like that. I did that once where i forgot to put back on the cap, started the car, and the idle would sputter about. Replaced it and it was cool... the oil cap should always be on...
    1995 325i Automatic-283+k Miles-Dinan Engine and Tranny software-PRM Intake w/ECIS Heatshield-HKS Klasse Exhaust-Motorsport X-Brace-Sparco Strut Tower Bar-M3 Rear Sway Bar-UUC Tranny Mounts and Enforcers-InPro Ellipsoids w/Umnitza DDE Angel Eyes-M3 Oem Front-M3 Side Skirts-M3 Trunk Lip-M3 Rear Bumper-ACSchnitzer Roof Spoiler-18'' Hamann HM2

    Quotes: "Old age and treachery will always overcome youth and skill"

    "No Fat girls please, my car will scrape"

  3. #3
    Join Date
    Jan 2003
    Location
    Pittsburgh, PA
    Posts
    1,146
    My Cars
    With the cap off the engine is ingesting air that has not been metered by the mass air flow sensor and it will idle a little rough. It should never be removed with the engine running anyways.

  4. #4
    Join Date
    Mar 2004
    Location
    Warren, NJ
    Posts
    183
    My Cars
    2008 BMW 135i - Stage 1+
    I like to check for blow-by, and listen for strange noises... That's why I take it off when I'm checking out a car..

    Thanks for the replies....

    Dave

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