Proper Way to Set Idle Speed on a 3.0 QV

Discussion in 'Mondial' started by Albert Penello, Mar 18, 2020.

  1. Albert Penello

    Albert Penello Karting

    Jul 21, 2019
    Woodinviille, WA
    Full Name:
    Albert J Penello, Jr.
    I'm looking at Page D52/D53 of the Workshop Manual and the process for setting the idle speed is VERY different from what I've read online.

    This is made more complicated by the fact that the pictures in the manual are from the older 3.0 and 8 models with a much different throttle body.

    According to the workshop manual

    "The idle speed will be adjusted by the throttle screws (B) (see fig. 41). The By-Pass screw is normally closed; use it only in case it is impossible to balance the vacuum with the throttle screw only."

    Ok so when I look at the picture -
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    The "bypass" screw is in a different place from my car.

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    But the parts are called the same thing on both diagrams.

    This would suggest the correct method to set idle is to close the bypass screw and adjust the other one.

    Does this mean I should be closing the bypass and adjusting the idle using the screw located at 18?

    This goes against everything else I've read - but this was taken right from the workshop manual!
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  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    Full Name:
    Steve Magnusson
    #2 Steve Magnusson, Mar 18, 2020
    Last edited: Mar 18, 2020
    The WSM was written at a single (early) point in time (when K-Jet without Lambda was just introduced) -- things/procedures evolved from there (and your '85 US version 3.0 K-Jet with Lambda is a bit different using a different throttle assembly which is why your screws B & C are in different locations than what's shown in the WSM). I believe the more recently accepted method would be to use the throttle plate screw (with the bypass screw fully closed) to get something like ~700 RPM warm idle and then open the bypass screw to bring it up to 1000 RPM (with the O2 sensor unplugged). (You could probably get either method to work OKish -- the bypass screw is just another airflow path in parallel with the throttle plate airflow path.)
  4. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    Austin TX
    Full Name:
    Brian Crall
    Ferrari taught us a different way and it makes more sense. I have no idea why the book says what it says. Idle should be around 750-800 with the idle air bleed closed and the mixture correct. Then raise the idle via the air bleed screw to 1050-1100 with the mixture correct. Do this with O2 disconnected then reconnect O2 and reset to 1050-1100.

    The mixture with CIS will vary dramatically with small changes in RPM at low RPM and trying to adjust by ear is a waste of time. It is far too sensitive.

    If you have a throttle switch insure that it is on the idle contact when finished. Also insure the throttle stop is resting on the screw and the throttle switch is not acting as a throttle stop. They will be very close to each other.
  5. Albert Penello

    Albert Penello Karting

    Jul 21, 2019
    Woodinviille, WA
    Full Name:
    Albert J Penello, Jr.
    Perfect thanks very much! It was nice this afternoon so brought out my Vac gauge, Innovate LM2, and Timing light (for more accurate RPM)

    I also wanted to wait until I got the new O2 sensor installed as well as the test pipe and the Nouvalari Exhaust so I was tuning to my final exhaust setup.

    The car was warm from a drive but I let the car heat up until the fans come on (just under 195). Removed the O2 sensor plug.

    Final values are

    14.0 AFR (1.3 CO)
    1050 RPM (using bypass screw)
    10 Hg of vacuum from plenum.

    Idle is steady, vacuum is steady and throttle response is good.

    Looks like I'm on target based on the WSM!
  6. spicedriver

    spicedriver F1 Rookie

    Feb 1, 2011
    As long as you don't have a cat installed, you can swap out your WUR for a vacuum enrichment type WUR, and simply disconnect your frequency valve electrical connector. It's easy enough to swap back if you have to take an emissions test.
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