My 96 chevy runs rough and backfire/surges on slight acceleration. Only codes are for random misfire. I monitored live data and found short term bank 2 at -12% and long term at -10% thus running rich. But bank one short term is normal. I removed the upper intake and took out all the injectors and primed the fuel pump but none of them showed any leaks. Anyone have any ideas on what could cause this?