I don't think the grill block would effect it. I would re-install the block.
There was probably a problem in that the EGR not functioning properly due to the exhuast leak. This might throw the fuel trims way out of line, (not enough exhuast in the intake air), throw the check engine light you were seeing, and prevent lean burn.
Mind you, that's all supposition from a computer engineer, not an automotive one...
YMMV, etc...
Throw the grill block back in,and see what happens? Only costs you a bit of time, and some skinned knuckles worst case?
-Steve