I don't think anyone is picking apart your installation. I just think there is something that is messed up that you have not identified yet. I don't think you could get so lean as to not idle. Lean is going to show up under load. You are heading down an expensive path that might not be necessary.

That said, your description sounds like a post-MAF air leak. I think Dallas is on the correct path. The sensor is setup to read the incoming air based upon the cross-section of the stock MAF. Same sensor in a bigger hole is going to give you a reading that under estimates the actual amount of air flow. Also, how is the sensor sealed in the larger MAF? Any other places for leaks between the MAF and the TB?

Good Luck,
Michael