air in brake lines but no work has been done to the brake system! What could cause this?

I have seen this happen if the brake fluid gets low. It can pull in just a little air when the reservoir gets low and get in between the fluid. Very rare occurance but I have seen it.

You may have more than an air problem. On my corvette, I found out that the rubber hose that goes between the metal brake line and the brake caliper can and will expand under hard braking over a period of time. Solution is to use a braided stainles steel hose in place of the rubber hose. My question is if you did no work to the brake system, how did you know or come to the conclusion that the problem is air. if bubbles come out during bleeding than that is air in the system and something may have an extremely small leak but like the othe answer, this is very rare.

Pedal just went to the floor, felt like air. So I bled the system and can not get the air out of it. So I'm thinking a component has a problem. I've checked for leaks and can't find any.

That is a hole different story! You needed to provide this info. first. It is probably a busted brake line due to rust. Fill it full of brake fluid,put the cap back on,pump the brakes 10 times and see where the fluid runs out.If it is full of fluid and no leaks,the master cylinder is bypassing and needs replaced.