bank 2 too lean engine light

[theSpoon]

so all winter i've been getting one engine code in specific, "bank 2 too lean" and "P0420" for my cat efficiency, i still get the efficiency code but since replacing the crank case vent tube, which I had previously removed and replaced with a filter, the "bank 2 too lean" code stopped showing up.
Has anyone else had this happen? could putting that tube back have fixed my lean condition? the hole on the intake tube was plugged so the only un-metered air going in would have to be through the crank case vent. Recently the weather has also gotten warmer which could have contributed the code not coming up anymore. I just want to know if anyone knows about this, I may do the fuel filter and O-ring seals on the intake just to be on the safe side, but if a filter on the crank case could cause a lean condition it would save me some trouble.

 

[birdfalk]

Check all you vacuum lines, that was the culprit for me.

 

[theSpoon]

it seems to have gone away since I put the crank case vent tube back on and threw out the filter I put on there, does that tube affect the vacuum ? I had plugged the hole on intake tube when it was off.