Weird problem
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Cadillac DTS Forum - 2006 through 2012 Discussion, Weird problem in Past Cadillac Vehicle Discussion; So on Thursday morning I was heading to get mt car state inspected. It started running strange almost like it ...
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    Weird problem

    So on Thursday morning I was heading to get mt car state inspected. It started running strange almost like it is misfiring. The car is not throwing any codes. When at a stop light the car seemed to want to go. It was lurching forward even though my foot was firmly on the brakes and the throttle was closed. This same thing happened to my '02 Seville and it was the intake plenum. So yesterday I went by the dealer and picked up a plenum. This morning I removed the intake manifold to find the plenum in good condition. No tears and seemed to snug up nicely. So I figure it might be a cracked spark plug as that has happened to this car once before. So I change out all 8 spark plugs with AC Delco 41-987's. Problem is still there. Then I decided to clean the throttle body as I had cleaner within arms reach. The problem is still there.

    Since I am not getting any codes I am at a loss as to where to check next. Does anyone have any ideas? I could start throwing parts at this thing and eventually I will get it fixed. But that will be expensive. Any input is greatly appreciated

    Don

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    Re: Weird problem

    Power Brake Booster,maybe?

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    Re: Weird problem

    A little more info. I drove the car to the store and the engine got fully up to temperature. Once up to temp the problem seems to go away. That is what lead me to believe it may be a cracked spark plug. But when I pulled out the plugs none of the insulators had cracks.

    Don

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    Re: Weird problem

    When at a stop light the car seemed to want to go. It was lurching forward even though my foot was firmly on the brakes and the throttle was closed
    That sounds like the throttle position sensor. What are your rpms at idle? What happens if you put it in neutral, foot off the gas? When the TPS went bad on my DeVille, the rpms would jump up to 2000 in neutral.

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    Re: Weird problem

    Quote Originally Posted by Tom's Caddy View Post
    Power Brake Booster,maybe?
    This is definitely an engine issue not a brake issue. I did check the vacuum hose for cracks and didn't feel any

    Don

    ----------

    Quote Originally Posted by ral1960 View Post
    That sounds like the throttle position sensor. What are your rpms at idle? What happens if you put it in neutral, foot off the gas? When the TPS went bad on my DeVille, the rpms would jump up to 2000 in neutral.
    Idle stays fairly steady. If the car is in park or neutral no noticeable change in RPM but you can feel the "stumble". I just wish a code would set already so I know where to look. I think I may just throw a MAP sensor in there and see how that does. Not sure that will do anything but they are pretty cheap

    Don

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    Re: Weird problem

    So, what exactly is the problem? Patient presents with vague symptoms, asks for a half dozen medications.

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    Re: Weird problem

    #PIP3146D: Rough Idle Crank No Start Extended Crank Or Misfire When Cold Due To Sticking Valves Or Excessive Carbon On Top Of The Valves - (May 11, 2011)
    Subject: Rough Idle Crank No Start Extended Crank Or Misfire When Cold Due To Sticking Valves or excessive carbon on top of the valves
    Models: 2000-2012 All Passenger Cars with Gasoline Engines
    2000-2012 All Light Duty Trucks with Gasoline Engines



    This PI was superseded to update recommended field, model years and engine list. Please discard PIP3146C.

    The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
    Condition/Concern:Rough idle, misfires, extended crank, or crank no start when cold. The engine may run rough for up to 5 minutes after starting the engine and may exhibit a P0300 DTC too. This may be caused by sticking valves or excess carbon due to fuel contamination
    Note: fuel oxidation and volatility concerns can often cause these issues as well, however they cannot generally be checked in service. Trying a different, high quality fuel is sometimes the best diagnostic.

    When the engine is cold, the compression on multiple cylinders may be at 0 PSI. The engine also may pop through the intake or exhaust while cranking and the spark plugs may be fuel fouled when inspected. Some engines may also experience valve damage or cam followers that are out of position as a result of this.
    This condition can occur in specific areas of the country for a period of time and then it will no longer occur after the suspect fuel source has been consumed in that area of the country.
    Recommendation/Instructions:If the SI Diagnosis leads to a compression loss due to sticking valves, the following information may help:
    If there is no sign of valve damage or cam followers that are out of place, perform the following procedure to free up sticking valves and to prevent the valves from sticking again. If valve damage is present or if there are cam followers that are out of place, perform engine mechanical repairs as necessary to correct the concern and then perform the procedure below to prevent the valves from sticking again.
    • Clean the fuel system by following the applicable "Fuel System Cleaning" procedure outlined in SI.
    • Add fuel injector cleaner "GM Fuel System Treatment PLUS, P/N 88861011 (for U.S. ACDelco, use 88861013) (in Canada, 88861012)"... see This PI was superseded to update recommended field, model years and engine list. Please discard PIP3146C. bulletin # 05-00-89-078B, to the fuel tank in the approved quantities.
    • Refill the fuel tank using fuel from a high volume, high quality filling station.
    • Clean the induction system using GM Top Engine Cleaner. Follow the directions on the can but DO NOT force the engine to stall since forcing the engine to stall with liquid Top Engine Cleaner could cause the engine to hydro-lock. * If available use an atomizer with Top Engine Cleaner through the throttle body.
    • Advise the customer to change fuel filling stations. They should use fuel from only high volume, high quality filling stations or they should use a Top Tier Detergent Gasoline if available. See 04-06-04-047I (U.S.) or 05-06-04-022G (Canada) for details regarding Top Tier Detergent Gasolines.

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    Re: Weird problem

    Bad gas was going to be my second guess.

    What octane fuel do you use? I've tried 87, 89, and 93 in the last month and can't tell much difference, except in the price.

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    It's almost impossible to find "bad gas".

    Octane is NOT the problem.

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    Re: Weird problem

    So impossible they wrote a PIP about it, whatever that stands for. Gas will go bad if it sits for months, just ask my lawnmower. That's one reason they recommend high-volume stations.

    I was asking a general question about octane. I can't detect any difference. I'm wondering if anyone else does.

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    Re: Weird problem

    Quote Originally Posted by ral1960 View Post
    So impossible they wrote a PIP about it, whatever that stands for. Gas will go bad if it sits for months, just ask my lawnmower. That's one reason they recommend high-volume stations.

    I was asking a general question about octane. I can't detect any difference. I'm wondering if anyone else does.
    Speaking only for myself and my car... I can detect a very noticeable difference.
    Both Performance and fuel mileage suffer.
    My fuel mileage will drop about 10 to 12 percent when using regular vs Premium.
    Performance also takes a VERY noticeable hit.

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    Re: Weird problem

    Quote Originally Posted by ral1960 View Post
    I was asking a general question about octane. I can't detect any difference. I'm wondering if anyone else does.
    Not to hijack this thread but octane ratings has been discussed in a number of threads. Short synopsis - there are two camps: one like Superjim who find a difference, and the other like me who sees none. As I'm a cheapo I stick with 87 and have never had low mileage, pinging, or lack of power.

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    Re: Weird problem

    I use 87. Always have always will. I used 93 in my Seville several years back for three tankfuls to see what the difference was. If I remember correctly I do believe that 93 octane, and a light right foot, netted me 1/2 mpg increase. So back to 87 for me. Anyway, this morning the wife and I were driving to go to breakfast, and a telling symptom happened. At a stop light, with the car misfiring which the wife felt, two messages came up. Service stability system and traction control. This same thing happened to me when I had a cracked spark plug. So now, since I changed out all of the plugs yesterday, I am thinking I have a bad coil. The same coil that was with the cracked plug (number 4) looked quite rusty. So I ordered an AC Delco coil while eating breakfast and when it gets here I will start with number 4. If that doesn't fix the issue I will change out the coils one by one until I find which one )if any of them) is the bad one. I also ordered a new MAP sensor last night so when that gets here I will change that out too. But I do believe that iy is going to be a coil

    Don

    ----------

    I use 87. Always have always will. I used 93 in my Seville several years back for three tankfuls to see what the difference was. If I remember correctly I do believe that 93 octane, and a light right foot, netted me 1/2 mpg increase. So back to 87 for me. Anyway, this morning the wife and I were driving to go to breakfast, and a telling symptom happened. At a stop light, with the car misfiring which the wife felt, two messages came up. Service stability system and traction control. This same thing happened to me when I had a cracked spark plug. So now, since I changed out all of the plugs yesterday, I am thinking I have a bad coil. The same coil that was with the cracked plug (number 4) looked quite rusty. So I ordered an AC Delco coil while eating breakfast and when it gets here I will start with number 4. If that doesn't fix the issue I will change out the coils one by one until I find which one (if any of them) is the bad one. I also ordered a new MAP sensor last night so when that gets here I will change that out too. But I do believe that iy is going to be a coil

    Don

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    Re: Weird problem

    Those aren't the messages one would expect from an engine problem.

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