Car shuts off every 10 min or so.

I purchased a 2002 a6 quattro with 140000 miles. It ran great for the first two months. One day I went to start it and it just wouldnt even tho it was getting spark and fuel. I waited twentry minutes and it started right up. This happened once or twice a week for two months. Recently it has progressed and only runs for ten minutes before shutting off even while driving. I replaced the fuel pump and filter and the problem persists. The check engine light was on due to a catalytic conv issue but no other warnings pop up. I have no idea where to look next. I was told its my security system cause my key fob doesnt work, or my intake is leaking. I am an idiot with cars n have no idea, please assist.