Alright, I just recently replaced my thermostat housing, and literally upon driving out of the shop i started to notice a rough idle, at first just when in park, but now when in drive at a stoplight. My first thought was to replace the plugs, clean MAF & throttle body, but now im throwing codes for System too lean for both bank 1 &2. I also have cat deficiency codes for cat 1 &2 as well. What should i tell my mechanic to look at first? THANKS!!

 

What engine? If the 4.4 I would look at the EGR system. The bolts in the far back can be loose and cause a leak. Or when you did your housing something was not plugged in fully, etc.

 

PLEASE make sure to reset the system before you get too far down the road trying to diagnose this. I had the same issues (almost exactly) after removing the TB to clean and also install the T-Stat housing and went through a living hell trying to diagnose those codes. Once I finally reset the system with the IIDTool, all was good. It needed to relearn the Throttle Body.