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85 308 GTS QV Idle Issue

Discussion in '308/328' started by Salbones, Sep 10, 2019 at 1:34 PM.

  1. Salbones

    Salbones Rookie

    Apr 14, 2019
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    Salvatore Celeste
    My idle speed is "hunting" high and low about 150 rpms either way, otherwise, the car runs perfectly. Has anyone encountered this up and down idle and if so, what did you do to correct it?
    Thanks,
    Sal
     
  2. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    1. What version '85 308QV? US, euro, something else?

    2. Was everything OK and then this problem suddenly started, or has it had this problem consistently since the last time it was "adjusted"?
     
  3. 308 milano

    308 milano F1 Rookie
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    Jan 15, 2007
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    Kim
    Had this issue once with my 84 GTB QV US version. Turned out to be rubber horse became disconnected under the coolant expansion tank on the left side of the engine bay closest to the trunk. Can’t remember at the moment what the piece is called that the tubing was connected to but it gave me those exact symptoms. Note: this happened suddenly, from one day to the next.
     
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  4. thorn

    thorn Formula 3
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    Aug 7, 2012
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    Tallahassee, FL
    I'm going with vacuum leak.
     
  5. Salbones

    Salbones Rookie

    Apr 14, 2019
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    Salvatore Celeste
    US Version, all OEM. I noticed it when it was brought out of storage last spring.
     
  6. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Does it display this (bad) symptom:

    A. During both cold idle (coolant temp less than about 140 deg F) and during warm idle (coolant temp above about 140 deg F)

    or

    B. Only during warm idle (but not during cold idle)?
     
  7. Salbones

    Salbones Rookie

    Apr 14, 2019
    7
    Full Name:
    Salvatore Celeste
    Just during warm idle.
     
  8. Steve Magnusson

    Steve Magnusson F1 World Champ
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    This is somewhat good news as it shows that the basic open-loop portion of your K-Jet system is working OK, but that the "Lambda" portion of your system is having a problem.

    Things I would check:

    1. Throttle microswitch operation -- At warm idle, the idle switch portion of the throttle microswitch should be closed. This connects the black wire in the harness on terminal 18 to the pink-black wire in the harness on terminal 2 = this "tells" the injection ECU: "I'm at idle so limit the excursion of the frequency valve to limit the swinging of the air-fuel ratio at idle". Unplug the throttle microswitch (item 48) at warm idle, and use a jumper wire to connect the female terminal 2 in the harness connector (the pink-black wire) to the female terminal 18 in the harness connector (the black wire) and see if that has any effect. Also try using the jumper wire to connect the female terminal 2 (the pink-black wire) to ground (the bare metal of the engine block or cylinder head) to see if that has any effect. If neither has any effect (plug the throttle microswitch back in) go to test 2.
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    2. Improper O2 sensor operation -- The O2 sensor could be bad, or you could have an air leak into the exhaust stream that is "fooling" the O2 sensor, or the air injection system could be improperly staying "on" during warm-running. First thing to do here is give the exhaust system and the air injection system a good inspection to look for air leaks. Very common for the check valves (items 3) or the air injection manifolds (items 4&5) to get rusty and break or develop holes. Also check the conditions of rubber hoses (items 6), especially where they connect to the hot check valves, and rubber hose 9:
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    If everything seems physically OK with the exhaust system and the air injection system, at warm idle:

    2A. Unplug the small vacuum hose (item 14) from the top of the cutoff valve (item 1). The logic here is that during cold-running there should be vacuum present on that small vacuum line = opens the cutoff valve = allows air to enter the air injection manifolds (but during cold-running the injection ECU ignores the O2 sensor signal so this is no problem). During warm-running, there should be no vacuum on the small vacuum line (item 14) = leaves the cutoff valve closed = no air enters the air injection manifolds = O2 sensor signal is valid for the injection ECU to use. If no effect go to step 2B.

    2B. Remove hose (item 11) from the airbox and physically block it closed or squeeze it closed (ensuring the same as a correctly closed cutoff valve during warm-idle). If still no effect, trying a new O2 sensor would be my choice. If still no joy = you don't want to go there...
     
  9. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Forgot to add that it wouldn't hurt to also unplug/replug the connector on the K-Jet with Lambda ECU in your RH rear trunk area just to rewipe those connections. Additionally, your schematic shows a common grounding point with many wires associated with this injection system connecting there -- wouldn't hurt to unbolt/clean/retighten (if you can find it -- its position on your schematic implies it is either in the rear trunk or engine bay, but, hopefully, another Owner can post its actual location). Good Hunting!
     
  10. Salbones

    Salbones Rookie

    Apr 14, 2019
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    Full Name:
    Salvatore Celeste
    Thank you so much for such a detailed explanation. I just got back from a short vacation (why the slow response) and I plan to go through these steps starting tomorrow evening. I will let the group know how it goes...Again, Thanks for great (And very detailed) advice!
     

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