The 355 'spider' idle stumbling problem is solved!!!! | Page 4 | FerrariChat
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The 355 'spider' idle stumbling problem is solved!!!!

Discussion in '348/355' started by gothspeed, Jul 23, 2007.

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  1. No Doubt

    No Doubt Seven Time F1 World Champ

    May 21, 2005
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    Mr. Sideways
    #76 No Doubt, Apr 15, 2014
    1995 was Motronic 2.7, same as latter 348s. 1996+ was Motronic 5.2.

    Besides the air circ issue, a low battery or weak alternator can cause idle stumble (Motronic adjusts the fuel map based on system voltage)...especially when something substantial such as the cooling fans kick on.
     
  2. johnk...

    johnk... F1 World Champ
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    Jun 11, 2004
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    John Kreskovsky
    #77 johnk..., Apr 15, 2014
    Yes, I am aware of all that and I understand the electrical issues which could result in stumbling. But if the air recirc issue is a root cause all such cars (96-87) should suffer it, no? And by your own statement re electrical issues it would not seem appropriate to just jump in and perform this mod without checking into those other issues. I'll have to check the recirc thing on my 95. It may not suffer the problem but it should still exhibit the back flow when the fans kick on. Same fans, same ducts.

    I'm rather pragmatic about such things. If A, B, and C can cause D I'm want to know where the problem is before I implement a solution. Not much sense in modifying the radiator shroud if the problem is a bad air temp sensor or dirty MAP or weak generator or battery...
     
  3. gothspeed

    gothspeed F1 World Champ

    May 26, 2006
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    goth
    #78 gothspeed, Apr 15, 2014
    Last edited: Apr 15, 2014
    This finding was not a 'fly by night' troubleshooting endeavor. There was a lot of time methodically spent and the 'finding' was confirmed and repeated on more cars than I can recall. You are more than welcome to test this for yourself ...... preferably on a 1996 - 1997 with the 4 slat duct, as those are the models I found had this issue. As I have mentioned: "this is 'one' cause of that idle stumble and 'one' solution ..... there are other factors which may also be at play .... like a weak alternator, bad ground(s) or fans which draw too much current for whatever reason etc."

    Also as No Doubt stated, the 1995 model is 2.7 Motronic vs the 1996 1997 is 5.2 ....... in addition to the different intake/temp sensor configuration, I am fairly certain there are a few differences in programing 'logic' as well.

    .
     
  4. No Doubt

    No Doubt Seven Time F1 World Champ

    May 21, 2005
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    Mr. Sideways
    #79 No Doubt, Apr 15, 2014
    Motronic 5.2 uses O2 sensors both before and after the cats, so it stands to reason that 5.2 is more voltage-sensitive than 2.7, which merely looks at one side of the cat exhaust.

    The car alarms on the 5.2 cars seems to create low battery conditions more frequently, too...so those models are primed to experience the idle stumble bug.
     
  5. John Glen

    John Glen Formula Junior

    Dec 30, 2009
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    John Glen Wesanko
    #80 John Glen, Apr 15, 2014
    Hmmm, excessive current draw when fan kicks on, fuses blowing, high current draw causing stumble in idle. Change out the junk fan motor and I bet your problem goes away. Just my opinion, I may be wrong ?
     
  6. Bobtifft

    Bobtifft Rookie

    Nov 20, 2010
    1
    #81 Bobtifft, May 18, 2019
    Yep, I will confirm this fix! You are a god send. We were chasing everything on this problem from voltage problems, electrical interference from electric motors in the ecu circuit to maybe a cam timing problem from last "major". After reading this, I decided to go out to the car and just disconnect the intake tubes from the cowl intake to the air boxes and just run intake side of air boxes open. Boom! Car ran perfect at idle, fans on, fans off, air conditioner on, air off. I am just going to leave it. No reason to get air from the doors.

    Thank you my friend
     
    No Doubt likes this.
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