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308 Cold idle problem...?

Discussion in 'Technical Q&A' started by FerrariFrank1, Aug 22, 2004.

  1. FerrariFrank1

    FerrariFrank1 F1 Rookie

    Aug 15, 2003
    3,887
    Chicago-Phoenix-L.A.
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    Frank
    I just developed something on my 1981 308GTSi that I was wondering if anyone knew about. The car is all original. Still has the Air Pump,everything. Just turned 20K Miles. Has about 3 years and 6K on the last belt service. It will be going in for a 30K, plus anything else it may need in a few months.

    But,twice now,when I first start it up...the initial "Cold Idle" doesn't kick down. It usually does after a couple of minutes...less when it's Hot out. I had to turn the car off,then restart it and it was fine. I had the Rear deck lid opened,and noticed both times that it happened, that a plug or something that is connected to the left side of the exhaust manifold gets,literally,Red Hot. Thats when I immediately shut the car off. (and this happens,maybe after only a minute or two longer than a "Normal" start.)

    This hasn't happened all the time. I have started the car several times between incidents with no problem.

    Any suggestions as to what this problem is,before I just take it in...?

    Thanks!!!!!!!
     
  2. DGS

    DGS Three Time F1 World Champ
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    May 27, 2003
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    All my manuals are in transit storage, but it sounds like perhaps the thermo-time switch is cooking itself?
     
  3. M.James

    M.James F1 Rookie

    Jun 6, 2003
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    Michael.C.James
    I thought the Thermo Time switch was in the radiator??? There's one in the exhaust manifold, too? Isn't that the O2 sensor?
     
  4. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Your particular K-Jet injection system has 2 thingys for allowing extra air into the intake system when cold to raise the RPM:

    1. Aux. Air Valve -- a slow-acting open-loop device, and

    2. Cold Start Air Valve -- a more complex, quick-acting device that has a lot of upstream electro-pneumatic gizmology to activate/de-activate.

    I'd go with something in the #2 system as a first guess (see page 68 in the 216/81 OM). If one of the lines passing air thru the cold start air valve (when it's supposed to be open) is a flexible line, you can try just pinching that air line closed from the outside to block the airflow when you're having the problem (warm, but high idle) -- if the idle RPM drops then that's the area to pursue.

    You can do the same "pinch" test on the air lines passing thru the AAV to rule that in or out.
     
  5. CarlH

    CarlH Karting

    Feb 5, 2004
    81
    MD
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    Carl H.
    Just went through a similar issue on my 83. My experience with the CSAV is the vac pressure closes the valve, so pinching it off would not change a stuck open valve. My issue was that the thermo switch was never activating and the valve stayed open, and RPM's were 2700 all the time. I took the vac input off the thermo switch and ran it into the CSAV and corrected the problem. (normally the output line from the thermo switch runs into the CSAV) I suppose if the car were tested for emissions at cold idle, i would have a problem, but for now it runs fine.
     
  6. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Carl -- I'm not talking about pinching off the vacuum control line, but rather pinching off the main air conducting line (i.e., blocking the extra airflow directly).
     
  7. DGS

    DGS Three Time F1 World Champ
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    May 27, 2003
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    I only have manuals for the 328 and the carb (78) 308 on CD. But on the 328, the thermo-time switch is in the block, not really all that close to the manifold, but I couldn't think of anything else near the manifold from memory.

    After checking the manuals, ... the "air pump" and "cold start air valve" make me think that the 308i may vary significantly from the 328 (which I was pretty sure is similar to the QV).

    But if the 308i has an air injection system, I'm wondering if maybe one of the check valves has gone bad, allowing exhaust gasses to pass back into the inlet, and getting the check valve hot. I can't really see the O2 sensor on the 328 from above the car, but anything (like the cold start (fuel) injector) that had the car running too rich might cause that to heat up a bit -- but you should get the "slow down" light before it got that hot.

    But it's sounding like the 2v 308i may differ significantly from the 328 (and QV?), so I'll leave this to the experts, as the only "books" I have with me are the scans I burned onto CD-ROM.
     
  8. FerrariFrank1

    FerrariFrank1 F1 Rookie

    Aug 15, 2003
    3,887
    Chicago-Phoenix-L.A.
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    Frank
    Thanks Much for the replies...Now I have a trail to follow...:)
     
  9. CarlH

    CarlH Karting

    Feb 5, 2004
    81
    MD
    Full Name:
    Carl H.
    Steve - Sorry.....Did not realise which air line you were talking about. My mistake!
     

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