rough idle
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5.0 and 5.7 Discussion, rough idle in Cadillac Engine Technical Discussion; when the car is cold or only slightly warmed up my car barely idles and sometimes even dies. i noticed ...
  1. #1
    89fatb's Avatar
    89fatb is offline Cadillac Owners Fanatic
    Automobile(s): 1989 fleetwood brougham 145k
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    Oconomowoc, WI
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    rough idle

    when the car is cold or only slightly warmed up my car barely idles and sometimes even dies. i noticed that if i cover the carb with my hand it idles beautifully. that leads me to believe its running lean. the question is if it is running lean or if the idle speed is incorrect? is the ilc plunger suppose to be against the throttle lever, cuz its not...btw it does fast idle when i pump the gas when i get in the car, its when i kick it down i have these problems. choke opening too soon?


    thanks guys for all the help i have recieved in the past, i really got to get around to posting a pic of my ride

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  3. #2
    carnut is online now Cadillac Owners Master
    Automobile(s): 1988 Allante' (sold), 1984 Eldorado, 84 Sedan DeVille
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    Re: rough idle

    These chokes do open quickly by nature, so as to not let the engine run too rich too long (emission rules) I would verify the secondary choke break is adjusted to the proper setting. The service manual speaks to a certain drill bit diameter that is inserted between the carb bowl and the choke blade. If that distance is too great, the choke blade would go vertical too quickly and if it was not great enough the engine would load up. I'm thinking that distance needs to be closed a bit. My other thought is to pump the throttle to set the choke then once running, put in gear and drive away, dont kick it down. Once you apply throttle to drive away the fast idle would drop a bit anyway and it might help the transition from cold engine to warm engine. Also verify the door in the air cleaner snorkle is closed upon cold start. If staying open all the time, it would cause cold running driveabilty stumbles. That flexible hot air tubing to the aircleaner is there to provide hot air to the carb only during cold start, then the door opens in the air cleaner and fresh air is allowed to the carb.

  4. #3
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
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    Re: rough idle

    I was thinking the same thing, I have fussed with the initial choke opening on mine as it was a 350 in place of the 307 so mine had to have some slight tweaking. It needs to open to around 0.1" within a couple seconds off cold start (primary vacuum break, aka, choke pull off opens this up right away). The secondary vacuum break is delayed by the ECM to around 30 seconds, depending on temps (we aren't having warm ones right now here!). It starts to pull a little bit more and at that point the choke probably isn't getting warm just yet, maybe, it is in the exhaust stream there. Make sure there is no vacuum leaks on the choke hot air tubes too.

    You set the primary vacuum opening with the phillips screw there on the pass side. Turn it clockwise just a little. See if that helps.

    At fast idle the ILC won't be pushing on the throttle, as the vacuum will be keeping it fully retracted. The fast idle screw is down underneath, pass side on the primary throttle blade shaft. I tweaked mine to be slightly lower than stock to keep it from racing at cold startup.

    I have the FSM for the 85 if you need any procedures or dimensions. For the "Y" 307 it should be the same as 89

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