Merc 225 idle problem

[txdrew]

I running a 99 merc 3.l 225 EFI with a list of performance upgrades, including a WT tuner. Last weekend I broke a section off my midsection at the front of the cav. plate, (you can see the water pump for the lower unit.) At or about this time I starting having idleing issues, low idle, keeps dieing out at idle. My question is this problem related to the hole in mid, is it caused by more or less back pressure to idle correctly or is it something else? Performance is down by 3-4 mph.Compression is good across the board, no miss or anything.
Any suggestions?
Thanks, Drew