HELP! erratic idle
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, HELP! erratic idle in Past Cadillac Vehicle Discussion; Hi guys, I am a bit new to the Cadillac world so please bare with me. I have a 2001 ...
  1. #1
    63chevy is offline Cadillac Owners Member
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    HELP! erratic idle

    Hi guys,
    I am a bit new to the Cadillac world so please bare with me. I have a 2001 DeVille with a very erratic idle which is only getting worse with every attempt to fix the problem:

    The car runs erratic throughout the RPM range with idle speed being significantly worse.
    codes:
    O2 sensor
    cam position sensor
    torque converter
    TCC (transmission control computer) stuck off
    missfire bank 1

    In addition a loud hum and, in my opinion, an excessive amount of heat are coming from the right rear of the trunk (?thinking fuel pump?); also the micro relays under the rear seat are excessively hot.

    Probably unrelated, the car has suddenly begun to pull to the right with a noticeable vibration from the right front wheel.

    I have replaced the cam position sensor and the fuel filter.

    My thoughts are that having replaced the cam sensor with no positive effect the erratic idle is caused by a fuel issue, thus replacement of the cheapest component- fuel filter. Now it seems to run worse. With the cost of a fuel pump about $300 I'm looking for help before my wallet dies. Thanks for any input guys.

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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: HELP! erratic idle



    When was the last time you cleaned the TB?

  4. #3
    63chevy is offline Cadillac Owners Member
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    Re: HELP! erratic idle

    Probably 2002/2003. In fact I had thought about that the other day, and I guess promptly forgot about it; but I'll do that right now. On my other vehicles I clean them when I have another reason to take them off. Can i clean it while it's on the engine? Is there a prescribed method of cleaning? Thanks for the reply and the welcome.

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: HELP! erratic idle

    No need to remove it. Just block the throttle plate open, then...... well, you know what to do. I think there is a tutorial in the Tech Tips section if you need it.

    I assume you do not have a P0171 & P0174 code?

  6. #5
    63chevy is offline Cadillac Owners Member
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    Re: HELP! erratic idle

    HEY! I have both. haha. And then some:
    PCM: P0171, P0174, P0300, P0340, P0420, P0741
    I have looked them all up, and am trying to make sense of them all.
    bank 1 lean, bank 2 lean, misfire, cam sensor, cat system, TCC stuck off, respectively.
    With the 171 & 174 codes and the heat in the trunk the evidince is mounting for a new fuel pump. As for the 0741, the transmission shifts fine. So, I wonder if that's an errant code or of those trivial codes that sound important.

  7. #6
    basscatt's Avatar
    basscatt is online now Cadillac Owners Master
    Automobile(s): 89 Coupe DeVille, 95 Sedan DeVille, 03 SLS, two 02 DHS's
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    Re: HELP! erratic idle

    Quote Originally Posted by 63chevy View Post
    HEY! I have both. haha. And then some:
    PCM: P0171, P0174, P0300, P0340, P0420, P0741
    I have looked them all up, and am trying to make sense of them all.
    bank 1 lean, bank 2 lean, misfire, cam sensor, cat system, TCC stuck off, respectively.
    With the 171 & 174 codes and the heat in the trunk the evidince is mounting for a new fuel pump. As for the 0741, the transmission shifts fine. So, I wonder if that's an errant code or of those trivial codes that sound important.
    -----------------------------------
    you have a torn plenum - resulting in a huge vacuum leak -

    the plenum is the bellows-looking piece
    between the throttle body and the intake -

    with the engine running - spray carb cleaner in that area -
    if the idle speed increases - you found the leak -
    you might be able to feel it with your finger -
    the split is always on the bottom -

    there is a "HOW-TO" replace it in the "TECH-TIPS" forum -

  8. #7
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: HELP! erratic idle

    Yup, the plenum is your problem.

  9. #8
    63chevy is offline Cadillac Owners Member
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    Re: HELP! erratic idle

    Thanks for all the help guys. I could hear the air being sucked in, but I never would have found the tear without removing the plenum. It was right up against the flange from about 5 o'clock to 7 o'clock. once I gave up my great desire to not dismantle the intake system it was really pretty easy.
    The one problem I had was when I spayed the brake clean it was sucked into the combustion chamber and out came a very toxic cloud that permeated everything, and sent me out of the garage for some time. It's only too bad I didn't need to replace the starter, as I'm sure it will go out soon now that I have done all that work. Haha. Thanks again for all the help.

  10. #9
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: HELP! erratic idle

    You'd be surprised at just how long these starters last being tucked away high, dry and relatively cool (compared to being tucked under the exhaust manifold).

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