Help Diagnosing P0304 and P0300 (5 Viewers)

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Jan 27, 2025
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Seattle, WA
Hey all, hoping somebody out there can help me diagnose a constant misfire on my '97. First appeared driving on the highway and has been running very rough ever since. It never has problems starting up, but it's running real rough.

I've replaced spark plugs and injectors. I checked the other day and cylinder 4 has spark. When I did injectors, I took off the upper intake manifold, and it seemed like all the vacuum tubes and hoses were intact. I've also looked around for a vacuum leak and haven't found one. Did a compression test and had good compression. My next thought was that it could be fuel pump related, except the car smells strongly of gas which makes me think it's running rich and not lean. Wondering if bad O2 sensors could be the culprit, but before I pull the trigger on ordering new ones, I was reading about the VSV valve and coolant temp sensors, and it sounds like there could be a lot more potential causes.

Any help or links to other threads would be appreciated. I'm a piss poor mechanic but I'm trying to avoid paying someone else to fix this.
 
Did you change the plug wires when you changed the plugs?
When you changed the plugs, did you nice any oil around the drive hex?
 

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