Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurring" - Page 3
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Cadillac STS Forum - 2005 through 2012 Discussion, Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurring" in Past Cadillac Vehicle Discussion; I have the same issue with my '06 STS, code came up as throttle body needing cleaned, did that but ...
  1. #31
    1harleyman is offline Cadillac Owners Member
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    I have the same issue with my '06 STS, code came up as throttle body needing cleaned, did that but havent driven it much since, but what little i did it seamed to help so far.

  2. #32
    jasonjsimon is offline Cadillac Owners Member
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Quote Originally Posted by stevenriz View Post
    With 130k, I have a weird nose like a light "knock" or as I call it, slurring when driving 20-30mph with light pedal. Just like when coasting. Weird. When I let off or step on it to downshift, the knock goes away... Bad gas? I use regular... Timing problem?
    I have this exact problem with my 05 V8 with 145k. My symptoms are exactly as you've described. Gas is crap in Utah. Regular is 85 octane. My question is, how soon should I see an improvement in the knocking if I start using premium?

  3. #33
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    I'm not convinced there's anything wrong. The Northstar isn't the quietest engine, especially since they added VVT.

    If you haven't been using Top Tier gas, you'll need a throttle body cleaning before long. If you do, two tanks of premium is more than enough.

    Make sure to have the your codes read to be certain you havn't had un-noticed ignition issues. You're at the right time to start needing a xoil or two.

  4. #34
    jasonjsimon is offline Cadillac Owners Member
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Quote Originally Posted by EChas3 View Post
    I'm not convinced there's anything wrong. The Northstar isn't the quietest engine, especially since they added VVT.

    If you haven't been using Top Tier gas, you'll need a throttle body cleaning before long. If you do, two tanks of premium is more than enough.

    Make sure to have the your codes read to be certain you havn't had un-noticed ignition issues. You're at the right time to start needing a xoil or two.
    Thanks for the response. I will clean the throttle body and try a couple tanks of premium. I haven't got any codes right now, so I don't know of any other ignition issues.
    What are the symptoms of a bad coil?

  5. #35
    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    A coil going bad may cause an occasional miss or loss of power when hot (especially a 'heat soak' situation) or when cold & damp. Hard starts and other symptoms will usually set an engine light, but not always.

    If there really is anything wrong, the noise will get worse. I'd be surprised if it's anything major on these V8's. No worries!

  6. #36
    KRSTS is offline Cadillac Owners Enthusiast
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    A bad or failing coil pack will cause a misfire which will normally throw a code and illuminate the check engine light.

  7. #37
    fredolan is offline Cadillac Owners Member
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    I just posted this in the knocking thread.

    I had the problem with "knocking" whenever I used less than premium fuel (I know, I know, its in my head. . . but it wasnt). I only use 93 octane. This problem was noticed when I first bought the car in 2006 when it had about 40-50k on it. It now has 211k and I just started to hear this knocking again despite the high octane fuel. It is very subtle and most people probably wouldnt notice it. It only "knocks" when there is a very slight pressure placed on the accellerator. In "accelleratio" it does not "knock" at all. I will probably have it looked at and then post what I find. I am hoping to drive this car for another 100k. . . .I hope. It has been an excellent vehicle all around.

    Also, I had plugs replaced recently (I have never used anything but OEM) and am very particular about oil level. Only use Mobile 1 oil and change it religiously. I doubt these are related. It has gotten very cold out in Michigan recently. . . .
    For me this "knock" seems to come and go. I'll re-post if I get any answers. Regards, Bob

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