1FZFE runs rough 4 minutes into warmup, intermittent

[landbruiser96]

Hi All, my otherwise always perfectly smooth running FZJ80 recently started missing, losing power and running rough about 4 minutes after starting. Began as the temperature guage jumping all over. It was the wiring harness, close to the EGR where it goes through the intake plenum was abraided and grounding out. Fixed that, but the rough running when warm persists. On initial startup, it always runs like a Swiss watch, then about 4 minutes in, it's like a switch comes on causing it to run like crap. A coolant temp sensor, maybe? Another short? Cleaned the throttle body and the mass airflow meter, new cap&rotor, plugs are good. What else? Thanks Mucho.

 

[Fj80oregon]

Unplug your upstream o2 sensor and see if that changes it after it’s warmed up. Report back after

 

[landbruiser96]

Unplug your upstream o2 sensor and see if that changes it after it’s warmed up. Report back after

Yep, that was it. I removed the sensor and it was black. The condition seemed to coincide with a lot of idle time this winter when it was in the -40's to -60's below zero, just plugged it up from not warming up to O.T. Cleaned it out with some CRC MAF sensor cleaner and it went back to running like a Swiss watch w/256K on it. Got a couple new oem O2 sensors on the way just for good measure, it's probably time for both. Thanks again- really appreciate your insight

 

[petegangies]

I was going to say o2 sensor for sure, but @Fj80oregon beat me to it haha! Don't you just love an easy diagnosis and fix?