355 Rough Idle and bouncing at high rpms | FerrariChat
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355 Rough Idle and bouncing at high rpms

Discussion in 'Technical Q&A' started by Miniwerks, Oct 10, 2005.

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  1. Miniwerks

    Miniwerks Formula Junior

    May 13, 2005
    270
    Sacramento, CA
    Full Name:
    Mike McCormick
    #1 Miniwerks, Oct 10, 2005
    My 95 F355 is idling rough all of a sudden. Starts up fine, idles smooth when cold, run it briefly and idles rough, doesn't stall just rough. Bounces a little at higher rpms for example when holding idle at 5000rpm. One plug wire was arcing, fixed the wire but that didn't fix the idle. Plugs are fine, compression fine all around, O2 sensors fine, OBD scan was clean, didn't pick up anything. It acts like a vacuum leak. We don't have an SD2 tester and not sure what to look at next, any ideas? The mechanic does not think it is related to throttle body balancing, I already mentioned that to him.
     
  2. jeffdavison

    jeffdavison F1 Rookie

    Jul 29, 2002
    2,544
    Suwanee Georgia
    Full Name:
    Jeffrey Davison
    #2 jeffdavison, Oct 10, 2005
    check the fuel filter..may need a new one.

    jd


     
  3. f355spider

    f355spider F1 World Champ
    Owner Rossa Subscribed

    May 29, 2001
    18,055
    USA
    #3 f355spider, Oct 10, 2005
    I have a 97 with the motronic 5.2, and had a wandering idle problem...would occaisionally hang at 1300 or even 1400 rpm, other times drop to 700 rpm. I cleaned and treated the mass air flow sensor connector with Stabilant 22, and that fixed it. You have two on the 2.7 car, I would try that.

    Most of the threads I have read here on rough idle issues are invariably related to bad plugs or bad wires. I would check them again carefully. One option is just to replace all the wires, just to be sure. You can get a full set of new ones from www.kingsborne.com for $150 with factory oem Beru connectors. Only issue is they use red wire, so you must special request black wire if you want it to look oem. I haven't tried these yet, but other have and say they work fine.
     
  4. jeffdavison

    jeffdavison F1 Rookie

    Jul 29, 2002
    2,544
    Suwanee Georgia
    Full Name:
    Jeffrey Davison
    #4 jeffdavison, Oct 10, 2005
    Could also do the Coil on Plug conversion..

    :)


    JD

     
  5. wildegroot

    wildegroot Formula 3
    Professional Ferrari Technician

    Nov 19, 2003
    1,522
    Frenchtown NJ
    Full Name:
    Wil de Groot
    #5 wildegroot, Oct 10, 2005
    I would think about replacing the plug wires too if they look aged even a little bit or don't Ohms test well. I would also clean the throttle bodies very well and make sure they are synchronized CORRECTLY.

    Wil
     
  6. No Doubt

    No Doubt Seven Time F1 World Champ

    May 21, 2005
    72,740
    Vegas+Alabama
    Full Name:
    Mr. Sideways
    #6 No Doubt, Oct 10, 2005
    The difference between the good idle when cold and the bad idle when hot is the closed loop of your ECU's for your A/F mixture.

    Your exhaust ECU's set a signal that tells your A/F ECU's to switch from open loop mode (essentially a pres-set factory condition) to "closed loop" mode.

    Once in "closed loop," your ECU's look at your O2 sensors' data as well as your MAF (MAFs plural for a 348). Likewise, your cold-start components are turned off.

    If your idle was rough all of the time, hot and cold, then I'd look for things like a clogged fuel filter, dying fuel pump, clogged air filter, etc...but if you are doing fine when cold and only having a problem when hot, then I'd look at the circuits that are in play when hot.
     
  7. Miniwerks

    Miniwerks Formula Junior

    May 13, 2005
    270
    Sacramento, CA
    Full Name:
    Mike McCormick
    #7 Miniwerks, Oct 10, 2005
    Thanks for all of the great input, I will share with my mechanic tomorrow. I definitely learned a few new things. Thanks, Mike
     
  8. f355spider

    f355spider F1 World Champ
    Owner Rossa Subscribed

    May 29, 2001
    18,055
    USA
    #8 f355spider, Oct 11, 2005
  9. jeffdavison

    jeffdavison F1 Rookie

    Jul 29, 2002
    2,544
    Suwanee Georgia
    Full Name:
    Jeffrey Davison
    #9 jeffdavison, Oct 11, 2005
  10. jh355

    jh355 Formula Junior

    Feb 12, 2004
    424
    Halluci-Nation
    Full Name:
    Craven Morehead
    #10 jh355, Oct 11, 2005
    Dave, where did you purchase the Stabilant 22? I need to perform the same repair, but first must charge the battery and put air in the tires, Lol.

    J
     
  11. f355spider

    f355spider F1 World Champ
    Owner Rossa Subscribed

    May 29, 2001
    18,055
    USA
    #11 f355spider, Oct 11, 2005
    Locally, you can get it from a VW dealer or NAPA store, but most do not stock it, and will have to order it for you. I think VW had the better price of the two. You can also order from our sponsor Ricambi America: http://snipurl.com/iedd
     

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