Ok then this is a wierd one. when the motor is nice and hot, say in sat in traffic the O2 sensor go to a lean reading and stay there untill the jeep has been turned off and left for some time. Now here's the really strange bit, these sensors should read between 0 and 1 volts. 0 being lean, 1 being rich. When it plays up on mine it will read -4 volts, yep that's right minus 4 volts. Ideas anyone? :(thinkhard):