Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurring"
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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; With 130k, I have a weird nose like a light "knock" or as I call it, slurring when driving 20-30mph ...
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    stevenriz is offline Cadillac Owners Fanatic
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    Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurring"

    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?

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    josephdav01 is offline Cadillac Owners Member
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    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 had knocking at 80k and I was using regular. I know u can use regular but my caddy didn't like it. I switched to premium and now I have 101,000 miles on my car and haven't heard the knocking since.

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    EChas3's Avatar
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Steve - If you aren't using Top Tier gas, that would be the first change I'd recommend. If that's not convenient, consider adding some Techron and/or Throttle-body cleaning. If it persists, Try mid-grade or premium.

    You could just go to premium and then work backwards, but under those conditions, I doubt you'd really be doing any harm. (I have heard that noise on those rare occasions when I burn crappy E10+.)

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    stevenriz is offline Cadillac Owners Fanatic
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Hey guys. Thanks for the tips. I'll try premium and see what happens. What will it cost me, an extra $2/tankfull? I'm also thinking about the about the plugs that are still original. Could old plugs cause this do you think? Should I replace them? Next tankful will be premium. I normally use Mobil.

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    EChas3's Avatar
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Exxon Mobil is Top Tier. Unless your car has close to 100,000 miles, I wouldn't recommend plugs. If you do change them, use OEM. N* is fussy about plugs.

    Living in MA, you might be in an area with a crappy gas formulation. Is it all E10?

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    http://pure-gas.org/

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    IF this is knock/detonation...

    If the engine has just started doing this, then the problem is not 87 octane, and masking the problem with higher octane won't fix the problem.

    Have you pulled codes?

    When was the last time the engine saw some WOT?

    What happens when the engine is under load? Knock usually doesn't occur under light throttle.

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    stevenriz is offline Cadillac Owners Fanatic
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Lost my post... Retyping...

    I exclusively use Mobil. Not always high test, mostly regular. WOT? Wide Open Throttle? every once in a while I do it but not often.

    This knocking does NOT occur under load. Only when coasting under light load at about 20-30mph. I am noticing now that there is a quick knock between shifts.

    I will bring it in and see what the dealer tells me :|

    I will report back what the resolution is!!

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    stevenriz is offline Cadillac Owners Fanatic
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    To answer another question, it is all E10 here in the Northeast I believe. I am only looking at the plugs for misfiring due to age. They may not work that way. Not sure.

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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Well your plugs should have been changed at 100k using only OEM plugs as the N* is very picky about its plugs.

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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    I wonder if this occasional noise is related to the VVT? I sure hope it's not piston slap.

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    stevenriz is offline Cadillac Owners Fanatic
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    What is VVT? variable valve timing?

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    curtc's Avatar
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    Quote Originally Posted by stevenriz
    What is VVT? variable valve timing?
    Yes.
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    Akatate is offline Cadillac Owners Member
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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    OP, I am having a similiar problem just recently with my '06 STS V6. I have just hit 80,000 miles. At cold start, primarily, low RPMs or cruising at higher speeds but only (like you said) when I lightly press the gas, I hear a knocking/slurring sound and a choking acceleration. Almost like having bad gas.

    When I floor it, no problems what so ever. But especially when I am leaving my neighborhood in the morning, anytime I slow down and start to accelerate, it knocks and gets choked up a little.

    I was thinking either fuel filter, injector or spark plugs. I changed the Air filter and am changing the fuel filter in the morning, but after reading this forum, I have little hope of this resolving the issue.

    If anyone has any suggestions, I would greatly appreciate it. Ive only had the car since September, 2012, and I would hate for this to turn into a major problem bc this car is a dream.

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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Akatate,

    Your experience is very different than mine. I've never heard what I've described when the car is cold or within 15 minutes of cold. When I have heard it, it's on the way back to work after lunch. The engine is essentially warm, but maybe not quite hot.

    I've never noticed any affect on performance, hence no concerns on my part.

    Make sure the oil level isn't low, it affects the VVT. Have you had your car on a code reader? The V6's often log valve timing sensor codes.

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    Re: Weird knocking when coasting 20-30mph with light pedal; almost like car is "slurr

    Also keep in mind the V6 lacks a low oil level sensor so actually open the hood and check it, so don't rely on an idiot light that doesn't exist.

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