1999 Audi A4 Brakes acting weird.

I have a 1999 Audi A4 2.8 Quattro and about 2 weeks ago I have been noticing something wrong with my brakes. After a long period of no driving, usually after night, I go and start my car and my brakes go all the way to the floor. But heres the kicker, after a short period of "driving" my brakes return to normal and dont malfunction for the rest of the day. No matter how many times I shut down my engine. Also, I recently had my rack and pinion replaced and ever since then my ABS light has been on. Now I was told to check and see if my ABS did work and it does, so its not the pump. I thought of my master cylinder was the cause, but since I get the brakes back, now I am not so sure. I thought of my booster, but I have no problem pushing the brakes in. I checked for leaks near the calipers and for under the car and none exist. Also my entire air mainframe has been replaced within the last year or so, so air within the system from with the air mainframe is minimal. And mechanically speaking, once brakes are restored then they work normally. The only ideas I have is that maybe I need to power bleed the system, but I just dont know.

Can anyone help me. I dont know what is going on.