Correct idle rpms for 425 engine?
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500, 472, 425, 368 Discussion, Correct idle rpms for 425 engine? in Cadillac Engine Technical Discussion; I was just wondering, what should the rpms be at for fast idle, idle in park (engine at operating temp) ...
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    caddydave2001's Avatar
    caddydave2001 is offline Cadillac Owners Fanatic
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    Correct idle rpms for 425 engine?

    I was just wondering, what should the rpms be at for fast idle, idle in park (engine at operating temp) and idle in drive? Seems to me my car idles pretty rough, especially in drive, and perhaps my idle is set too low? Im going to time the motor(found the vacuum leak finally) and I know its supposed to be 23 @ 1600 rpms, but I was curious of the rest. Thank you in advance.

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    carnut is offline Cadillac Owners Master
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    Re: Correct idle rpms for 425 engine?

    So raise the idle a tad to see if its smoother. 23 degrees at 1600 RPM? wheres that info from? All the idle speeds are listed in a carb overhaul kit, see if the parts house has a kit, read the numbers. Also a factory shop manual would list them as well. Any SMOG repair station in your area must keep a manual listing those specs. Ask to be allowed to read it.

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    Angry Matt's Avatar
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    Re: Correct idle rpms for 425 engine?

    As far as I know you should set the idle in drive with the vacuum advance plugged and that should be 600rpms. Isn't there specs on the sticker under the hood?

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    caddydave2001's Avatar
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    Re: Correct idle rpms for 425 engine?

    The specs Im getting are from the sticker under the hood. Ill write down all the information I have on there, and see what you guys think. Some of the desciptions are what have me guessing what they mean. But it does say timing to be set 23 degrees at 1600.

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    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Correct idle rpms for 425 engine?

    Actually, there are several required settings and I have them all saved on a disk somewhere. They are listed in your service manual under the description of your carburetor settings, which I use for this application. I don't have the manual here. If I remember, I'll look it up tommorrow.

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    awadecki is offline Cadillac Owners Enthusiast
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    Re: Correct idle rpms for 425 engine?

    you are correct about the timing on these...i was surprised to see the spec too on my 78 eldorado. anyway, good news is it works. the timing advances about 12 degrees from idle to 1600 rpm. i timed mine by holding the cruise control servo to speed up the motor with my right hand and the timing light in my left.

    by the way, i've found it also helps to block off the egr passage on these motors. the compression ratio is too low for any spark knock, although i do run midgrade just as a precaution. getting rid of the egr will make part throttle operation seem peppier. you might also have a rough idle because the egr is stuck open.

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