Help please with identification of what appears to be a faulty lambda sensor on my Citroen Xsara 1.4, TU3 with Sage SL96 ECU.
Originally checked it with Peugeot Planet and the lambda voltage at idle was jumping all over the place, from 100mV to 900mV and the engine missing and shaking too.
Did a quick swap with a spare lambda from my Gti6 and the idle settled and had less of a misfire but was running rich and indicated on P.P with a pretty constant 450mV.
Bought another NTK sensor for my car fitted it and went back to misfire and rough idle again, checked P.P and now the voltage does not read, just 000v, with a 'permanent high or open circuit' fault message.
Replaced the sensor with another new one and hey presto, exactly the same thing. So now have put back my trusty old 306 one in despite it running rich and burning fuel until I can find a replacement one that works.

The original lambda that was on the car was AFS 91, which cross checking on the NGK NTK comes up with part number 7979, which is what I tried but did no work.

Could I have a faulty ECU?, or should I try another model of sensor?.

Luckily the motor factors are just next door to my work, have already returned one on Saturday, don't know what they will say when I return the second one.

Yep tried that, temperature values are showing in Lexia (just realised I mentioned Peugeot Planet in the thread), even plugged in a spare one I had to make sure.

Got another NTK model sensor for Citroen Xsara's, seems to run better, idles a little rough but not as bad as before, just need to check the live voltage readings in Lexia to make sure.