Proper Idle RPMS in park???
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500, 472, 425, 368 Discussion, Proper Idle RPMS in park??? in Cadillac Engine Technical Discussion; I finally got my 472 to roar to life and timed I'm just wondering now what the appropriate idle rpm ...
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    streetsweeper1970mdh's Avatar
    streetsweeper1970mdh is offline Cadillac Owners Member
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    Proper Idle RPMS in park???

    I finally got my 472 to roar to life and timed I'm just wondering now what the appropriate idle rpm should be when the car is in park, the book said in drive curbside idle should be 600rpm, yet when I get it to idle at 600rpm in drive and then I put it in park the idle shoots up to 900 to 1000rpms is this normal? I'm not really sure, any help would be greatly appreciated. thanks

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    limousine rider's Avatar
    limousine rider is offline Cadillac Owners Member
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    Re: Proper Idle RPMS in park???

    You may need a stronger throttle return spring. Your carb sounds like its not closing all the way a weak spring can cause this sometimes.


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    streetsweeper1970mdh's Avatar
    streetsweeper1970mdh is offline Cadillac Owners Member
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    Re: Proper Idle RPMS in park???

    thanks I will def give that a shot

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    Night Wolf's Avatar
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    Re: Proper Idle RPMS in park???

    my '79 425 was 600RPM also.

    This is with AC off, if AC is on, it'll kick it up another few hundred RPM.

  6. #5
    cadillacmike68's Avatar
    cadillacmike68 is offline Cadillac Owners Connoisseur
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    Re: Proper Idle RPMS in park???

    The engine settings as specified by GM is supposed to be while the car is in DRIVE. Look at your engine fan shroud for the settings decal. (You can get one from McVeys and no I don't work for them.)

    This is all from memory since I'm not at home and my car is in the shop getting paint / body work (but I've had 68-74 Cadillacs for nearly 20 years total and did a lot of tune up work myself back in the day...)

    The AC should be off, the air cleaner off, the vacuum advance plugged, timing b/w 5 and 7.5 BTDC depending on the year, idle mixture screws all the way out then turned in 1 or 2 turns in (depending on year), Dwell set at 30. Now, turn the mixture screws in until you get a 20 RPMm drop, then back off 1/2 turn (do each side), THEN use the idle screw and adjust to 600 RPM (69 & up) or 550 RPM (68) in drive.

    I think this is sort of correct

    In park it should jump up 300-400 RPM or so this is normal and it won't hurt the transmission.

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