first post, hope i do everything correctly. lol.
well,
my Max has about 209,000 miles, it idles perfectly, when you drive it softly (not opening up the throttle) it rides awesome. here's the problem though..

when it's cold, oh man it has power. BUT, once it warms up, it starts hesitating, misfiring (you can even hear misfire in the intake manifold, i believe) once it passes 3,000 RPM (it's embarrassing!) i get a Knock sensor code, and an O2 sensor code for bank 1 sensor 2. i replaced both sensors before the CC (please tell me if i replaced the wrong ones since there's a third one, didn't replace it cause i know it's just to measure emissions and luckily Florida doesn't do inspections) but i used A cheap sensor for a replacement (the one where you have to cut and splice the wire). i followed the color code for the wires (two white and one black), but the code still comes up and the car still runs like crap. (i even swapped the two white cables to see if it was my error, but i get the same result). can anybody help? it would be so much appreciated. thanks!

 

Sounds like the exact same thing that happened to mine. It was the mass airflow sensor.

 

If it was the MAF it would run poor all the time. What was the o2 code? O2 codex don't always point to the sensor. Typically a bad cat showed itself as you describe, runs ok cold then looses power once warm.

 

B1S2 is after the cat.

 

I agree with FreshRichie. I had the same issue, and it was the MAF.

 

Pick up a can of CRC MAF cleaner from the auto parts store. Give that a go, reset the cel and see if that helps. I typically clean my maf every 10k when I change the oil. I've got 224k on my max and the maf is one of the few things I haven't had to replace, knock on wood.