Rough idle
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Rough idle in Past Cadillac Vehicle Discussion; Ok so the head gasket job went fine. Car runs fine. Has rough idle though. Cleaned TB. Swapped out plugs ...
  1. #1
    Caddy-EaRL's Avatar
    Caddy-EaRL is offline Cadillac Owners Fanatic
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    Ok so the head gasket job went fine. Car runs fine. Has rough idle though. Cleaned TB. Swapped out plugs and boots at HG job, swapped out coil cassettes with known good ones on hand. Wondering if the injectors got slightly clogged while car sat about 8 months. Idles at 750 and its fine until it warms up and idle gets rougher the hotter it gets. Yet take the idle up to 1000 and its smooth as silk. Racking my brain here. This mornin I ran some top engine clean through the intake and am letting it set all day. Hoping the nasty ass valves get cleaned up a bit and will fix this rough idle.

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    hendershot15 is offline Cadillac Owners Member
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    Re: Rough idle

    check your IAC valve and clean the throttle body. I had a similar problem and replaced the IAC valve and problem was gone. I don't know if this helps but you can try it. You can remove the IAC valve and spray some cleaner into it and see if that improves anything.

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    Caddy-EaRL's Avatar
    Caddy-EaRL is offline Cadillac Owners Fanatic
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    Guess its possible, never really seen an iac valve cause a rough idle, usually makes the engine stall. Already cleaned the TB.

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    hendershot15 is offline Cadillac Owners Member
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    Re: Rough idle

    all I am saying is to check it. worked for me... disclaimer: I am no car expert in any means

  6. #5
    basscatt's Avatar
    basscatt is online now Cadillac Owners Master
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    Re: Rough idle

    Quote Originally Posted by Caddy-EaRL View Post
    Ok so the head gasket job went fine. Car runs fine. Has rough idle though. Cleaned TB. Swapped out plugs and boots at HG job, swapped out coil cassettes with known good ones on hand. Wondering if the injectors got slightly clogged while car sat about 8 months. Idles at 750 and its fine until it warms up and idle gets rougher the hotter it gets. Yet take the idle up to 1000 and its smooth as silk. Racking my brain here. This mornin I ran some top engine clean through the intake and am letting it set all day. Hoping the nasty ass valves get cleaned up a bit and will fix this rough idle.
    ---------------------------
    OK - since you've around the block more than once -
    I won't ask if the have checked for codes -
    I will assume you have - and there are none -

    it sure sounds like a vacuum leak to me -

    runs rich at cold start - so idle is smooth -

    leans out as it warms up - and runs rough -

  7. #6
    Caddy-EaRL's Avatar
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    Well it seems like the top engine clean has helped it. He drove it home and will let me know tomorrow.

  8. #7
    tatteddaddy87 is offline Cadillac Owners Member
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    Did the top engine clean work in the long run? I am wondering because i have a 99 eldorado with the same problem .i have replaced the intake manifold and the fuel pressure regulator

  9. #8
    JDemoney is offline Cadillac Owners Member
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    Quote Originally Posted by Caddy-EaRL View Post
    Guess its possible, never really seen an iac valve cause a rough idle, usually makes the engine stall. Already cleaned the TB.
    The IAC can cause rough idles. If you don't want to replace it, remove it and hit it good with some brake parts cleaner. Make sure it's COMPLETELY dry prior to reinstall..

  10. #9
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: Rough idle

    .......... and clean out the throttlebody IAC bore with TB cleaner and a fuzzy pipe cleaner from a craft store. That black top hat plunger on the IAC motor gets fluffed up, too.

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