Replaced Resistor/Now misfiring
 

2007 XLT, 4.6L...138k miles....finally decided to fix the a/c speed control not working on all settings and replaced the resistor with the factory stock. immediately following installation, i noticed a misfire that gradually got worse. i don't know much about car mechanic but always like the opportunity to learn by doing simple to moderate mechanical stuff myself.

Now, i can't figure out why the change in the RESISTOR would cause misfiring and with NO CEL for first 200 miles. Finally, when it does come on about 2 weeks later, it registers OBD codes P0174 (bank too lean) and P0153 (O2 Circuit Slow Response (Bank 2, Sensor 1). I've replaced the upstream O2 sensor, checked for vacuum leaks and seaform gas treatment. although it running better, still misfiring and this rattling sound when it stutters. no misfiring during acceleration only at idle (sitting and when let us on gas while driving) and more so when a/c is on. I've noticed a loss of power when taking off and an occasional faint smell of gas.

I can't find any instances online where someone has had the same problem. Any suggestions guys.

Put the old resistor back in, and see if its still doing it. Seems like it's just a coincidence that it started happening when you changed it. Really shouldn't be any reason to make it misfire.
What's the mileage on the Truck? Have you done plugs/boots/springs?

yes, i replaced with old one and sounded better but still had the issue so ultimately replaced with new one. sparkplugs changed 3 years ago and currently have 138k miles. i've also noticed ratting coming from the cat conv.

Would either of these cause the rattling sound that appears to be coming from the cat converter? i replaced the O2 sensor that was noted as bad and no drastic change.