Can any one tell me the symptoms when the lamba sensor goes wrong? I am running closed loop on a s8 ecu and the car was running rich with an erratic idle, i have checked things like map sensors, ignition amps, how can I check the lamba sensor functioning? , there are four wires on the lamba sensor the grey wire was wasn’t connected but when I connected this wire thinking that it maybe positive but the car cut out on doing this… is this the right wiring sequence. Black = ecu sensor wire number two on the port ecu plug. Two white one = positive the other white plus grey = negative.

Thanks

Sean