I have a 2004.5 LLY that I just found out my mass air flow sensor was bad in it,but never gave a check engine light or threw a code. How can this be? Is there anyway to check for this in the future?

Yes it can. It can read inaccurately or 'slow' causing air/fuel problem. Normally you can just clean them and reinstall, but sometimes they need replacing.

How do you go about testing for this?

Quick answer: by watching data readings via Tech2 or other dianostic device and comparing those readings to what a 'normal' reading would be......and experiance.

curious, how do you know it's bad?

I was getting a Suncoast G-Max kit installed and the guy doing the work was having problems with Suncoast's torque converter and Suncoast told him to check all the sensors. That is when he found out my Mass air flow sensor was reading zero.
I still think it should have thrown a code!

if it was really READING ZERO, it would throw a MAF-performance-related code.

curious, how do you know it's bad?

me or the OP?

if it was really READING ZERO, it would throw a MAF-performance-related code.

Should have, but I've seen stranger things happen.

me or the OP?

OP...how does he know it's the MAF with no codes...

clean it and try again, if you have a k&n make sure it's dry before you install as just a little oil will mess it up