I'm pretty sure it would make a difference. If you decrease the IFR, you would richen up. I do most of my tuning in open loop, and I know for sure you can tune away a vacuum leak. You don't want to do that obviously.
Easiest way is to smoke it for a leak, but if you just stick a rubber gloves over the throttle body and blow a little air into a vac line, you can make the glove inflate a little. It should pretty much stay inflated when you plug the vac line you blew air in. Well, unless you have a big cam. If it immediately deflates, you have a leak.
