Rough Idle 300 error code - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 12-27-2009, 06:39 PM   #1
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Default Rough Idle 300 error code

Help! Here'* how I got here. The car dies and will not start. I tow it home and it sets for 3 days. I try t ostart it after sitting fires right up but got a miss and CHECK ENGINE light. I got it scanned at the local auto parts. Error 300. So I replace the plugs and wires. #1 and #4 look wet with fuel. So I have an old set of coil packs from a parts car. I replace each of them. Still there. I get a used ignition module. Same thing. Missing like a champ. Checked the fuel pressure with it running 45psi. Whats wrong with it? Its a 98 SLE.

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Old 12-27-2009, 06:49 PM   #2
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Sounds like you got most of the issues. Check for spark at those plugs. Also try a compression test.
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Old 12-27-2009, 06:50 PM   #3
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I think you meant to say P0300. Random misfire.

Just to help us out better, have you done any modifications to your car?

Dan has a good article in the Tech Info area that pertains to the P0300...

https://www.gmforum.com/showthread.p...ighlight=p0300
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Old 12-27-2009, 07:05 PM   #4
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No mods at all. And your right with the actual code #.
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Old 12-27-2009, 07:06 PM   #5
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Why if its an oxygen sensor or something along those lines isn't there another code?
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Old 12-27-2009, 07:27 PM   #6
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O2 sensor only throws a code if it goes out totally. They can get tired and slow as they age.
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Old 12-30-2009, 09:58 PM   #7
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Ok guys. I went to Advance. Had the ignition module checked. it was bad. Had the other one I used as a back up. Bad. Bought a new one. Running better than new! Never thought they were both bad The 1-4 coil pack was getting no spark. Replaced it twice !st. It was the ignition module underneath. Thanks for the help.
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