R50 misfire on specific cylinder

[UpUp_Away]

I have a ‘98 Qx4 that I should probably sell or junk and just get a new car, but I grew up with her and it’s hard letting go. The latest issue that’s popped up is an intermittent p0305 code. The engine runs smooth, I can’t even feel the misfire, but occasionally, after about 100-200 miles, the code will pop up.

 

I did a replacement on:

 

-new AGM battery

-new spark plugs

-new spark plug wires

-distributor rotor and cap

-ran two consecutive tanks of Techron concentrate and then Redline fuel system cleaner

 

The engine runs even smoother than before and I figured I solved my issue. But about 200 miles later of constant commuting, as I was on the freeway, I saw the CEL come on, and sure enough…

 

Anyone have any ideas on the next step? What could be causing a misfire that I can’t even feel, on a specific cylinder?

 

Because of the new wires, plus, and other parts I don’t think the spark is the issue, although I can try to close the Gap a bit to get a more reliable consistent spark.

 

With the back to back cleaners I don’t know if the fuel injector is the issue either…

 

Attached are the photos of the freeze frame data

 

 

 

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[Slartibartfast]

All that's left is fuel mix or compression. Your short-term trims are way different side to side, that may have something to do with it--could be a vacuum leak, injector issue, something like that. Check your vacuum lines, including the one to the fuel pressure regulator at the back (also make sure there's no fuel in that line). Could still be the injector. I'd do a compression test before chasing the injector unless the spark plug shows a clear difference in fuel mixture on #5.

 

Was there any obvious difference in spark plug color when you replaced them? Any fuel smell in the oil?