Q: Have a 2004 Trailblazer with the 4.2L. Idles rough and throws a "P0300" "Engine Misfire" DTC... Suggestions?

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Car died on the wife a couple days ago, lost power, dash light came on to "stop engine" as well as "low oil pressure". Suggestion was that the fuel pump or filter were bad because of the power loss. Changed the filter, car started eventually and runs now. It's throwing a P0300 engine code and running rough. Trying to figure out where to look. I have had to replace a coil once, the code it threw then was cylinder specific.. Now it seems more generic...

My car has 149000 miles.
My car has an automatic transmission.

It sounds like you could be having an issue with your fuel system. It is possible that the replacement of the fuel filter helped the issue but did not resolve it completely. I would recommend having your fuel pressure tested by a qualified professional and have it compared to the manufacturer’s specification. If the fuel pressure is low, it is possible that the fuel pump or fuel pressure regulator could be causing this issue. If these parts turn out to be working properly, I would then check the injectors for proper function.

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