P0300 Random Misfire - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 49 (permalink) Old 03-18-2014, 05:16 PM Thread Starter
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P0300 Random Misfire

Today while driving my CEL came on so I got the car scanned. The scanner read P0300 Random Misfire. Lately at red lights I've noticed the feeling of a slight misfire that goes away when the RPMS go over 1000 or so. I have replaced the spark plugs with AC Delco Iridiums. I took pictures of the old spark plugs in case any of you thought they looked funny. A few months ago I had a check engine light for a bad thermostat so I was running rich. When replacing the spark plugs I noticed a tannish white paste inside the (spark plug boot???) I tried removing with a small flat head as much as I could. I also did a vacuum leak test around the manifold parts with silicone spray and the engine acted normal. I ran seafoam through the booster line as well because it was time to do so but I also wanted to see if maybe a little clean out would help the P0300 issue. I am currently waiting to see if the CEL returns during my 1 hour commute tomorrow but I was looking for some pointers and other things to look at if the issue occurs again.



Also, is anyones iPhone autoguide app closing out on them? Mine has been lately.


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post #2 of 49 (permalink) Old 03-18-2014, 05:35 PM
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You didn't mention cleaning of your throttle body, I would put that on the to-do list.

P300 random misfire is only valid if it is accompanied with an actual misfire count. If no misfire counts occurs on any of the cylinders during this misfire P0300 You should wait for an HO˛ error.

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post #3 of 49 (permalink) Old 03-18-2014, 05:39 PM Thread Starter
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Where do I get a misfire count? I also ordered ACDelco spark plug boots on Rockauto.com
Here are some pics. The spark plugs are probably 1-1.5 years old.



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post #4 of 49 (permalink) Old 03-18-2014, 06:23 PM
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Most code readers will show a bit lower a Misfire count for each cylinder. At least mine does.

By the way in my opinion those plugs did not need changing but an ounce of prevention is worth a pound of cure.

---------- Post added at 10:23 PM ---------- Previous post was at 10:20 PM ----------

The white gunk you see inside your spark plug boot is normal. Humidity mixed with white lithium boot sealer grease over time.

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post #5 of 49 (permalink) Old 03-18-2014, 06:32 PM
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good plugs still haha. Beware, the Ignition Control Module on that style ecotec is known to fail....ALOT. I've replaced it twice in the last year on my 04 Cavalier.

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post #6 of 49 (permalink) Old 03-19-2014, 07:09 AM Thread Starter
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So what else could be causing my issue and what can I do to resolve
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post #7 of 49 (permalink) Old 03-19-2014, 08:40 AM
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Its probably your coil pack. Replace it

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post #8 of 49 (permalink) Old 03-19-2014, 10:18 AM
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^^ this or injectors sticking. A Random/multiple misfire isn't just on one cylinder tho, that means it's mission across the whole board. I would look into cleaning those injectors first (pour a whole can of sea foam in your tank at your next fill up), then if that doesn't solve the issue, then you may have other issues. Could even be a sensor starting to go out, you just never know.

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post #9 of 49 (permalink) Old 03-19-2014, 03:57 PM Thread Starter
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Ugh I really don't want to just throw parts at it.
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post #10 of 49 (permalink) Old 03-19-2014, 04:48 PM
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Hey there Clarky215285,

I'm sorry to hear of your concern. I am not properly trained to offer technical advice but I will be glad to look into this for you. Please send a private message with your VIN, dealership name, current mileage, and full contact information if any extra assistance is needed. We look forward to hear from you!

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Have you checked into Chevrolet Owner Center? You can maintain service history, check on warranty or recall information, and more. Visit my.chevrolet.com!
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