308 QV and 328 What Is your IDLE RPM Setting? | FerrariChat
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308 QV and 328 What Is your IDLE RPM Setting?

Discussion in '308/328' started by Jerry458, Apr 30, 2025 at 5:36 PM.

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  1. Jerry458

    Jerry458 Karting

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    #1 Jerry458, Apr 30, 2025 at 5:36 PM
    Curious to see what other owners report as for idle RPM when the car is warmed up my 308 QV seems to run around 1200RPM -1400 which seems a bit high. I have my adjuster on the throttle body all the way out but I think 1200+ is a bit high at idle. What are you guys running and how can I get the idle to drop lower?
     
  2. gdl203

    gdl203 Formula Junior
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    #2 gdl203, Apr 30, 2025 at 5:54 PM
    There are two screws to adjust idle. Have you used both?
     
  3. rwbolt1

    rwbolt1 Karting

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    #3 rwbolt1, Apr 30, 2025 at 6:03 PM
    I don't know if adjustable, but on my '89, 1500rpm on a cold start for about 30-60sec, then drops to about 1000.
     
  4. Jerry458

    Jerry458 Karting

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    #4 Jerry458, Apr 30, 2025 at 6:06 PM
    the big ALLEN screw underneath i have not messed with it is hard to get a tool in their i just adjusted the spring loaded stop screw up top at the throttle mechanism side where the cable attaches. FYI the car is a EURO car and I read many threads that 1200-1400 is normal idle on a EURO QV but still seems high to me
     
  5. miketuason

    miketuason F1 World Champ
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    #5 miketuason, Apr 30, 2025 at 7:02 PM
    My cold idle is 1800 RPM
    hot/warm idle is 1000 RPM
     
  6. Rifledriver

    Rifledriver Three Time F1 World Champ

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    #6 Rifledriver, Apr 30, 2025 at 7:17 PM
    According to who? They are wrong.
     
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  7. Rifledriver

    Rifledriver Three Time F1 World Champ

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    #7 Rifledriver, Apr 30, 2025 at 7:18 PM
    Well not really. The air bypass is the adjustment screw.
     
  8. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #8 Steve Magnusson, Apr 30, 2025 at 7:50 PM
    Don't be too trusting of your tach in the dash -- would be better to measure the frequency of the RPM flywheel sensor signal and do some math, or use a digital timing light with an RPM function.

    With the air bypass screw (the big hex-headed screw) fully closed, adjust the throttle plate adjustment screw to give ~700 RPM warm idle -- then open the air bypass screw to bring it up to 1000 RPM warm idle.
     
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  9. gdl203

    gdl203 Formula Junior
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    #9 gdl203, Apr 30, 2025 at 7:58 PM
    no, the air bypass screw. You adjust it by hand to open or close and see the resulting idle rpm

    If you already have the throttle plate adjustment screw all the way closed, and the idle is still high, then you may want to turn the air bypass screw to see if you can lower the idle

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  10. gdl203

    gdl203 Formula Junior
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    #10 gdl203, Apr 30, 2025 at 8:00 PM
    Right. But the throttle plate adjustment screw will also change the idling rpm, right? By applying more or less throttle when the foot if off the gas pedal.

    sorry if I’m using incorrect terminology
     
  11. Jerry458

    Jerry458 Karting

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    #11 Jerry458, May 1, 2025 at 5:44 AM
    i am going to mess with this later today, are you guys adjusting this spring tension big screw with your fingers or your using a tool or some sort? i can not get any of my allen hex bits to fit into that screw head as it hits the fuel line and underside of the throttle housing. I think the hex is a 10mm

    also would I be screwing this Air Adjuster screw in or out to reduce idle speed just for reference?
     
  12. Jerry458

    Jerry458 Karting

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    #12 Jerry458, May 1, 2025 at 5:46 AM
    that bypass screw in your photo looks like a brass screw and is a HEX mine is a silver ALLEN head which is a PITA to move and get a tool on it with the angle. I can not screw it in by hand with my fingers it seems to tight
     
  13. moysiuan

    moysiuan F1 Rookie
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    #13 moysiuan, May 1, 2025 at 6:04 AM
    Show a picture of your throttle body and engine bay, the air bypass is there somewhere...
     
  14. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #14 Steve Magnusson, May 1, 2025 at 8:38 AM
    Last edited: May 1, 2025 at 8:44 AM
    My ex-CIS F had the larger hex head so I just used my fingers. You may need to something like cut off an Allen wrench if you've got the large round Allen head style air bypass screw. It may have not been moved in a long time -- so once moved, it may get easier to rotate.

    Screwing the air bypass screw in (CW) should reduce the engine warm idle RPM. Since you've already got the throttle plate adjustment screw backed out to minimum, you may need to do a little back and forth -- i.e., screw the air bypass screw in a little, if the warm idle RPM drops too much, screw the throttle bypass screw in a little to get more air going past the throttle plate. Keep doing that until the air bypass screw is fully closed and the warm idle is ~700 RPM -- then open the air bypass screw CCW to bring the warm idle up to ~1000 RPM. If you can't do that (i.e., the RPM stays high with both the air bypass screw fully closed and the throttle plate adjustment screw fully backed out) = you've got some other issue (vacuum leak, throttle plate bent, throttle microswitch, if so equipped, holding the throttle plate open,etc.).

    One other "complication" is that if you have 84-85 US 308QV, there is a throttle microswitch mounted to the end of the throttle plate shaft that can restrict the throttle plate motion so that needs to be loosened for this adjustment (and then retightened in the proper position with the throttle microswitch closed when done).

    (You should add year and version to the "308QV" in your FChat Profile.)
     

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