Cold Engine Misfire
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Northstar Engines and System Technical Discussion Discussion, Cold Engine Misfire in Cadillac Engine Technical Discussion; Hello all, I have 98 STS with 85K on the clock and since it's gotten cold here in Northeast Wisconsin, ...
  1. #1
    kingsize's Avatar
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    Cold Engine Misfire

    Hello all,

    I have 98 STS with 85K on the clock and since it's gotten cold here in Northeast Wisconsin, I have developed a misfire when the engine is started cold. The engine idle is somewhat erratic like it is trying to fine the correct RPM, but as it runs for a brief moment, the idle lowers and it runs rough. Once it warms up, it runs great. I was thinking maybe it is a vacuum leak, but I thought I would ask you guys first. It sets a p0300 code, but it won't tell which cylinder is having the problem. I just replaced the plugs, but it didn't help at all. Any help is much appreciated.

    Thanks,

    KS

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    elwesso's Avatar
    elwesso is offline Cadillac Owners Master
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    Re: Cold Engine Misfire

    Maybe a coil???

    The engine does run quite a bit richer when its warming up.....

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    Re: Cold Engine Misfire

    Have you replaced the wires?

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    Re: Cold Engine Misfire

    No, I didn't change the wires yet. I guess it's worth it, but I thought the wires would last longer. I didn't want to just throw parts at it until the problem was solved without trying to figure out the issue by the symptoms. Any ideas why it only idles rough when it's cold? Does the temp affect the wires?

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    Re: Cold Engine Misfire

    I'm really not sure if wires are affected by tempurature but I have found out the hard way that when they are old and then disturbed they are highly suspect. My car ran just fine til I had the fuel rail replaced. Then I (and many others) developed a misfire. Plug wires every time. That is why I asked if you had changed them. General consensus is, stick with OEM wires. Best price I found was at http://www.rockauto.com.

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    Re: Cold Engine Misfire

    Thanks Ranger. I guess I will try that. In the meantime, I may look into a possible vacuum leak somewhere. The way the idle lopes when cold, I think it may be something in addition to the wires.

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    Re: Cold Engine Misfire

    Lopping does not sound like wires. Don't want to start you an an expensive wild goose chase. That sounds more like a vacuum leak or an idle control problem.

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    Re: Cold Engine Misfire

    Today I took the beauty cover off and ran the car to see if I could hear of any vacuum leaks. Even after a visual inspection, there was no hissing or "air" sound to be heard. I'm staring to think that my problem is not vacuum related. The car did set another code today though:

    P0404 - Exhaust Gas Recirculation (EGR) Open Position Performance

    Does any one know if this means the EGR is bad?

    Thanks,

    KS

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    LCLCLC is offline Cadillac Owners Fanatic
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    Re: Cold Engine Misfire

    P0404 probably means you need to take the car out and do several wide open throttle runs to hopefully clean up the EGR valve.

    Reset the code. If it comes back, the EGR probably needs taken off and cleaned.

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    Re: Cold Engine Misfire

    It sounds like a sticking EGR valve. It just needs cleaning. Take it off and clean the pintle shaft up inside the cast passage in the base of the valve. Do not let solvent run down the shaft into the can of the valve as it will eat the insulation off the wire windings in the can and ruin the valve. An EGR valve that is sticking open can cause rough running at idle and stalling. I am all for running the engine hard as often as possible...but that is not likely to clean up the EGR valve. It has to be taken off and cleaned.

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    Re: Cold Engine Misfire

    Hey Guys,

    I just wanted to write back and say thanks for the help. I removed the egr valve and cleaned it well. There was a little "burr" of carbon in there between the mating surfaces of the pintle and the can that caused the pintle to not operate smoothly. After cleaning, the car runs smooooth, even when cold. With the car being up for sale, I want to make sure the car runs excellent for the new owner when I find one. I really appreciate the help guys!!

    Thanks,

    Kingsize

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    Re: Cold Engine Misfire

    Quote Originally Posted by kingsize
    Hey Guys,

    I just wanted to write back and say thanks for the help. I removed the egr valve and cleaned it well. There was a little "burr" of carbon in there between the mating surfaces of the pintle and the can that caused the pintle to not operate smoothly. After cleaning, the car runs smooooth, even when cold. With the car being up for sale, I want to make sure the car runs excellent for the new owner when I find one. I really appreciate the help guys!!

    Thanks,

    Kingsize
    Glad it worked out. Hope you are selling to buy another Cadillac. If not, we may have to hunt you down for treason... LOL LOL

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    Re: Cold Engine Misfire

    Even with my modded Q, i still lust for a 98 STS.....

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    Re: Cold Engine Misfire

    Elwesso,

    She's listed in the Cadillac Classifieds if you want to take a peek. I really wasn't looking to sell until May or so. Let me know.

    Thanks again!

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    NYAviator is offline Cadillac Owners Member
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    Unhappy Re: Cold Engine Misfire

    This is my first post - thanks to you guys, I diagnosed a code 2 wks ago & my wires and spark plugs (OEM platinum) were replaced. Yesterday AM my 97Eldo almost stalled when started (~10degrees NY). I now get P0603 and 300 (vacuum?) - how do I 'check the vacuum'?

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