I have a 91mustang lx that is having some power issues. Sometimes it runs like a champ and others like a chump. I pulled the codes and came up with a code 67 with engine off and 12 while running, so these would have no effect on a power issue. It seems like I lose about 25 ftlbs of tq but the engine still pulls smooth. I have replaced the O2 sensors, engine coolant temp sensor, and the maf is clean. I am at a loss can anyone help me?