1998 yukon Mystery p0300 and rough idle still

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OilBurner2003

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Some random unorganized thoughts…

Try graphing the trims to see how they trend when given more throttle. A vacuum leak would usually show positive trims trending to zero with increased throttle - not what you have, though.

Bank 2 looks to be somewhat more of a problem child than the other, and the bank 2 downstream O2 sensor is switching - implies a catalyst issue. A graph on that would help see how it compares to its upstream counterpart.

But, I’m not sure if a clogged converter would cause negative trims (oxygen sensor is reporting too much fuel so computer is cutting injector pulse time to reduce fuel). Hmm. Usually that’s a leaking injector but a valvetrain issue may be another possibility? Sticking valve or lifter maybe? Maybe others can chime in on that?

Have you done a compression test?

Definitely swap the two downstream sensors and compare the voltages. The bank 1 sensor looks to be dead and your testing looks to show good circuitry.
Hello sir, Figured I'd give everyone a update. Shop called me and said when someone did the timing cover they messed up the crank sensor somehow when they installed the oil pan and timing cover. I had a shop do the pan and the cover, the irony. I had misfires before that point, but they seem to know exactly what they're talking about. They said something about the crankshaft too, can't remember what. I know how scary that sounds lol, The sensor how it was installed, a wire to the sensor, and that's about it so far. They're still figuring out the o2.
 
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OilBurner2003

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Hey, that’s progress! Maybe they’ll be able to sort it out.
They said the Crankshaft gear wheel is loose? To my knowledge, I thought there was only a Cam gear and a crank gear, not a wheel of some sort. Regardless, they said that’s 100% the issue. Told them to fix it so I don’t have to deal with it anymore. I don’t fully understand what they’re talking about, but if it’ll fix it, I’ll learn about it when I pick it up.
 
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OilBurner2003

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They said the Crankshaft gear wheel is loose? To my knowledge, I thought there was only a Cam gear and a crank gear, not a wheel of some sort. Regardless, they said that’s 100% the issue. Told them to fix it so I don’t have to deal with it anymore. I don’t fully understand what they’re talking about, but if it’ll fix it, I’ll learn about it when I pick it up.
Well, weeks later, P0300 Is gone. They told me the crankshaft "teeth" That the crank gear slides onto was shaved off, messing with the crank sensor somehow. Crazy. No clue what happened, they couldn't give me a explanation. But it's fixed! Idle is still slightly rough, nothing a little seafoam can't try to fix haha. I guess moral of the story is if you've done all the work in the world, a scanner can figure out stuff faster than you can lol. Told me the crank signal was "Erratic." Great guys! I hope anyone going through this page has success before they have to take the timing cover off...Appreciate all of you fine gentleman. Gonna go fix my heater now.
 

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