I am working on a buddies 2011 sportster 1200. We replaced the rear head gasket, both rocker boxes, coil relocation kit, and ignition relocation kit also. After we put it back together it developed a rough idle after it warms up and almost stalls out. I pulled the codes and the only one that came up was P0131 (front oxygen sensor reading low). So I cleared the codes and switched them. The code did not pop back up but is still doing the rough idle after warm up and almost stalling. I has short yappie pipes on it. Any ideas? I am stumped here!!!!

 

Check to make sure the throttle body manifold head rubber o-rings are not causing an air leak.