So I know I need to replace the PCV but I am getting misfires in Colorado only when I'm topping mountain passes above 8000' or so.

I'm getting mix too lean code and O2 sensor code. Any suggestions?

--jephro

 

to the forum Jephro


Hopefully someone will be along with some ideas.

 

How many miles? start with the simple - look for vacuum leaks/ intake leaks. its possible the MAP (altimeter) sensor is at issue or the O2 sensor but I'd look for a small vacuum leak first. You may want to have a shop do a smoke test before replacing parts if you don't find something obvious.