I changed coils and plugs the other day on my 2001 expy 5.4 and i kept getting codes for the left and right bank lean but it's ran fine and idled fine, so today i went to check the vacuum hoses and found that i must have pulled out the PCV valve on accident. So i stuck it back in the valve cover and started it and now it idles real rough and sometimes stalls, so i pulled the PCV back out and it won't even idle. I had a new PCV lying around so i stuck that in there and it didn't make a difference. I know the IAC is the most commom culprit, but why would me reinstalling the PCV cause this

 

The elbow probably has a big hole in it. follow the pvc line around back of the throttle body where it pugs into the manifold. check that rubber elbow. Replace it if necessary..

 

Yep, most common problem with those symtoms.

 

i must have caused the problem when i plugged it back in but how in the world did it run without it plugged in

 

Just that little bit of movement and jarring around in the pcv lines during the plug change could have caused a weak dried up line too finally crack.

 

it ran disconnected for a weak i had it shoved next to the block

 

When it was laying on the motor it was probably still sucking through the PCV. When you re-installed it that is probably when the elbow or line broke/cracked--now it is sucking unlimited outside air.