I recently purchased an 04 Taurus with a 3.0 OHV engine. This car had not been started or driven in over a year due to a bad transmission. I started the car and it ran OK, replaced the transmission and again it ran OK for 50 or so miles. When starting it one morning it ran and idled rough, had spark knock and backfired through the intake and exhause. The codes indicate OX sensors were reading lean on one and rich on the other. Later I determined the gas had gone bad and turned to varnish so I cleaned the system and replaced the filter. The engine runs somewhat smoother but not much. I have several mechanics look at the car and all they can seem to tell me is that the OX censors are not reading correctly. Where can I go from here?