4.9 stumbling right off idle - Page 2
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 stumbling right off idle in Cadillac Engine Technical Discussion; I dont know if it will help but its worth a try and is fairly quick and easy, i would ...
  1. #16
    justin4yu is offline Cadillac Owners Member
    Automobile(s): 1992 Cadillac Fleetwood 2door sedan
    Join Date
    Jun 2010
    Location
    Yelm, Washington, United State
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    28
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    31

    Re: 4.9 stumbling right off idle

    I dont know if it will help but its worth a try and is fairly quick and easy, i would pull out your computer get the numbers off it and hit the bone yard to find a replacment, swap the prom and cross your fingers. Hope you have good luck.

  2. #17
    daniel58 is offline Cadillac Owners Fanatic
    Automobile(s): 58 Coupe Deville, 77 Coupe deville, 90 Deville
    Join Date
    Sep 2009
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    183

    Re: 4.9 stumbling right off idle

    As the prior post, I'm going to agree and go out on a limb here and say that is could be your ECM that is causing ALL of your problems. If you are going to a yard for other stuff perhaps you can find one of those as well. They are quite expensive to pay list ( cheapest I have found is Autozone $90) to just try, but with your on board diagnostics not working its a could be.

  3. #18
    the recluse is offline Cadillac Owners Connoisseur
    Automobile(s): 2002 STS, 1991 Eldorado
    Join Date
    Feb 2009
    Location
    Jacksonville, FL
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    1,013

    Re: 4.9 stumbling right off idle

    ECM can't be accessed without HVAC to even decipher if ECM is the problem; he can't pull codes. Problem is cyclical unless you replace HVAC controller...

  4. #19
    daniel58 is offline Cadillac Owners Fanatic
    Automobile(s): 58 Coupe Deville, 77 Coupe deville, 90 Deville
    Join Date
    Sep 2009
    Posts
    183

    Re: 4.9 stumbling right off idle

    Just to add to this discussion, my 90 4.5 has a positive backpressure EGR valve. This means a good EGR will not hold vacuum or work with a vacuum pump. Back pressure from the intake closes a bleed hole to make the thing work. It also has to get vacuum from the EGR solinoid which it does only on certain conditions such as decelleration etc. As long as the EGR is closed (not cloggged open with carbon) I think you can eliminate that as the cause of your stumble. I have a friend who is a ret. GM line tech looking at my 4.5 with similar problems. We haven't figured it out yet, carbon on the O2 sensor is making it worse but we don't know why its runnig so rich in the first place. I will keep checking back/ let you know if we make any headway on my car.

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