Well this cars back in, Still playing up.

The car is fine cold and through warm up. When hot it starts to surge (and possibly a random cylinder misfire) quite badly unless you drive on WOT when it seems to go OK and does not surge.

Had the car in this PM, Checked all the HT, Mechanical, checked various sensors etc etc which All appear fine.

When checking the fuelling/O2 sensor something very strange showed up (Well strange to me, Possibly some of you have seen it before.

Sensor came on line reasonably quickly, switched nicely at idle and cruise, Responded as it should to WOT and over run, recovered to switching reasonably and all looked good. As everything got hotter/ran longer it would stick high (rich) at idle but still respond if you promoted change and switch normally at cruise. As the car ran longer the trace progressively dropped to what I thought was a low signal. At this point I suspected wiring and checked all I could get too and any earth/power supplies I could find. Then, when cruised, it started to switch in a negative direction (Switching from 300mv down to -600mv) at cruise. Eventually the sensor sat at 0v and switched to -700mv when cruised???? The other channels (TPS and MAP) were still giving a sensible figure. Letting the car cool and trying it again it goes through the same process. Ive checked connections, swapped channels and leads around just in case it was a problem with the scope but the problem stayed with the car.

Anyone have any idea's what could be causing this? Any areas I should be looking at? I still dont quite beleive the results myself. Will get a trace in the AM and post if I can, Had to leave work in a rush as Im off to see Frank Massey give a talk.

Thanks.

Steve.