FRMUL8D

I'm posting this for my roommate. He's got a 93 Z28 A4 car that he picked up very cheap to do a head swap on (to fix a bad valve guide) and sell it. He put on the replacement stock heads, as well as some pacesetter long tubes, removed the EGR and smog stuff, and did the throttle body bypass. Put it all back together, seems to run steady and smooth, but the car wants to idle around 2500 rpm and it won't come down. If you try and give it any gas it dies. It's also running extremely rich. The car is running open headers until he gets to the muffler shop to have a y-pipe welded up. Is the high idle and richness due to the open headers? The oxygen sensors are in and connected. Also the airbox is off at the moment until he gets a coldair intake for it, would this also affect anything on a speed density car? Any input would be helpful. Thanks.