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Relentless P0300 code

gofast

gofast

New member
Hope someone can help. 2004 Monte Carlo SS supercharged. Rough idle, runs perfect from off idle to any rpm as long as it's not boosting. When it gets to boost it goes right back to its random misfiring. And sometimes shows a too rich code but only if it tries to boost for more than a couple seconds. It has a new cat, resonator, MAF, IAC, PCV, ICM, plugs and wires, and has updated PCM from the dealership today and still has the same problem. New head gaskets and intake gaskets less than a yr ago. Could it be a bad intake gasket or a warped lower intake manifold?

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No compression test yet because it runs great without boost. Don't know brand of plugs, just bought it with this problem and was told he tried new plugs and wires and they do look brand new. Wires are actually Delco so I'm assuming the plugs are too.

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Wire are AC Delco. All the other stuff is the new stuff I have done to it.

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I will do that but would that cause the rough idle and rough under boost?

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I will look. I was told the car ran great till it just started doin that one day and he put new plugs and wires on it and it still does the same thing.

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I hope that's not the problem. It runs strong and smooth as long as it's not idling or boosting.

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Found the problem, cracked head between #4 & #6 cylinders.

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The machine shop just said it was cracked between the #4 & #6 cylinders. I haven't seen it yet.

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Not between cylinders, that's usually between the valves. I would be interested in seeing what happened.

Jeff
 
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