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'91 TR Idle rpm 'wobbling' when cold

Discussion in 'Technical Q&A' started by Testa, Mar 31, 2004.

  1. Testa

    Testa Rookie

    Mar 28, 2004
    47
    Hello,

    with a '91 TR i have the following problem:
    The car starts easily and runs at a higher Idle rpm for some seconds. Then the rpm is going down to idle for some seconds. But this idle is not constant because the engine is going back to the higer idle rpm for about 2 seconds, goes down to normal, back to high idle for about 2 seconds and so on. After some minutes when the engine is warm enough this rpm 'wobbling' stops and the engine goes to almost normal idle rpm. With almost normal i mean aprox. 1100 rpm which is a bit higher than the around 950 rpm it should be.
    Accelerating the engine during the 'wobbling' phase with the throttle to about 1500 or 2000 rpm stops the wobbling until the throttle is released again.
    Any idea what the problem could be ? Auxiliary Air valve ? Warm up regulator ? Anything else ?
    Already searched in the archive but could not find this kind of problem.

    Thanks,

    Bruno
     
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  3. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    What version '91 TR?

    Also, are you saying that the warm-running is perfect? When coming to a stop (warm) does the RPM undershoot below the normal warm idle speed?
     
  4. Prova85

    Prova85 Formula 3

    Nov 13, 2003
    1,952
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    Kenny K
    Bruno, you are not alone. My 85 does this too but only if I touch/blip the throttle right after I initally start it. If I dont touch the throttle it starts and idles normally. When this does happen a light touch of the throttle to get the revs to about 1500 for 10-15 secs and all is well. And it only happens when it's bone cold from not running for a week or so. I dont worry too much about it

    Kenny K.
     
  5. Dr_ferrari

    Dr_ferrari Formula 3
    Professional Ferrari Technician Consultant

    Nov 2, 2003
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    Jim McGee
    the Tr will do that if the base setup is incorrect. to correct you must have someone set up the base idle and mixture including the balance of the banks.

    best regards, jim
     
  6. carguy

    carguy F1 Rookie

    Oct 30, 2002
    3,313
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    Jeff
    My TR does this too. I would love to hear of a "backyard" method for getting the base mixture settings close, and then balancing each side. Am I correct in that this can ONLY be done by a mechanic with the proper equipment?
     
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  8. Dr_ferrari

    Dr_ferrari Formula 3
    Professional Ferrari Technician Consultant

    Nov 2, 2003
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    correct, need at least a mercury column set, digital/analog multimeter, long 3mm allen, long skinny slotted electrican screwdriver, two #2 pencils with good erasers, and a lot determination. my opinion, best left to the expert.

    best regards, jim
     
  9. pdavis

    pdavis Rookie

    Oct 31, 2003
    37
    Morristown New Jersey
    Full Name:
    Preston
    I had the exact same problem on my late 88.5 TR. I took it to the dealer to have the base adjustment done and the car now starts and runs smooth as ever. Recommend you leave it to a qualified dealer that has the right tools for the job. pd
     
  10. Testa

    Testa Rookie

    Mar 28, 2004
    47
    What do you exactly mean with 'what version '91 TR ?'
    It's a Testarossa (with Kats), not a 512 TR if you are asking for this.

    A warm stop will result in a 'almost' normal idle which means the rpm is stable at around 1100 (which i guess is a little bit too high).
     
  11. Testa

    Testa Rookie

    Mar 28, 2004
    47
    Thank you very much for so many replys.
    I will follow your hint's and take it to a dealer for doing the base setup.

    Bruno
     
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  13. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Bruno -- I was trying to understand what configuration TR you have -- "version" defines what type of Bosch CIS injection system (K or KE), with or without cats, and with or without closed-loop Lambda (O2) sensor control. All TR are made to one version or another (but like all things F -- some weirdness allowed ;)).

    My question about the idle was more on the motion behavior of the tach needle during (warm) deceleration to a stop (not what the long-term warm idle RPM level is). Does the tach needle:

    1. Come down in a smooth regular fashion directly to the warm idle value, or

    2. On the initial way down does it go slightly under the warm idle value and then recover in a second or two back up to the warm idle value?

    I should have also asked if this poor cold running behavior started suddenly (i.e., it used to be OK, but went to bad quickly) or if it's just never been right. If it's the latter, I think you've got the right approach to follow jim's advice and get the base airflow/mixture set-up checked. If it's the former, your problem might more likely be some upstream electrical gizmology problem.

    You didn't answer the other question -- is the overall warm-running behavior OK/good?
     
  14. Testa

    Testa Rookie

    Mar 28, 2004
    47
    Steve,

    sorry i was thinking all the 91 TR's are equiped with KE Injection system.
    But anyway, mine has a KE and cats.

    Regarding the exact behaviour of the idle on a stop i have to check tomorrow, did not look at this today.

    The question if this problem was always there or started slowly i can not answered yet also. I got the car last november and since then it was parked in the garage. When i started it for the first time last weekend i recognized this problem.
    Today i had a chance to drive the car for the first time this year and found that after starting the problem was only there for some seconds, not for minutes as last weekend.
    (The car was running at idle for around five minutes because the clutch did not work good after this long time so i could not put in a gear).

    The overal warm running behaviour is good, idle rpm reading at the tach needle is a little bit above 1000 and stable.
     
  15. Testa

    Testa Rookie

    Mar 28, 2004
    47
    Steve,

    checked the behavior of the warm engine when releasing the throttle.
    Rpm goes directly to idle, not below.

    Bruno
     
  16. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Bruno -- The problem/defect I was thinking of for your wandering cold idle also causes the warm deceleration RPM undershoot so (unfortunately) you must have something else amiss -- sorry I can't be of any help...
     
  17. Testa

    Testa Rookie

    Mar 28, 2004
    47
    Hello Steve,

    no problem. On wednesday next week the TR will got to a dealer so a F-mechanic can have a look on it. I already talked to the mechanic and he told me that many TR's had such kind of problem.
    I will let you know next week what problem was found.

    Bruno
     
  18. Shamile

    Shamile F1 Veteran

    Dec 31, 2002
    6,563
    Lakeland FL
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    Shamile
    Dear Ferraristi,

    Hey....I've got this problem....when warm, a blip of the throttle sends the rpm under to where it almost " coughs " then back up to normal. What gives?

    Steve?


    Shamile
     
  19. Steve Magnusson

    Steve Magnusson F1 World Champ
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    (You know, they hardly describe how things are supposed to work when it's all working -- and they certainly don't describe well the effects of missing or corrupt input signals, but)

    You might try checking that the idle microswitch is working correctly. (With key "off") Unplug both injection ECUs and measure the DC resistance at one of the connector ends between terminal 1 and terminal 13 (there's a diagram in the injection section of the TR OM showing the terminal numbering of the injection ECU connector):

    1) With the throttle plates in their idle position, there should be reasonable continuity between terimals 1 and 13 -- doesn't need to be super low, but shouldn't be hundreds of ohms or more.

    2) When you start to manually open the throttle plates, there should be no continuity between terminals 1 and 13.

    The rotational position of the throttle microswitch's body is adjustable because you need the two events (throttle plates on their mechanical rest and the contacts inside the throttle microswitch closed) to occur simultaneously (and since the throttle plate mechanical position is adjustable/uncertain, the throttle microswitch has to be adjusted relative to them).

    Probably a whole bunch of other horrible things that can cause a similar symptom, but I'd start with this (especially if your report is that it doesn't do this when "cold").
     

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