Lambda light - on my Sport that had a misfire for years

[rogerthechorister]

Some of you may remember my VERY long thread about my first 940 Sport Edition - N plate, standard. She had a misfire that eluded many attempts to locate it until the FOURTH AMM I tried and she liked that.

On Saturday I started her to drive the nearly 100 miles to Harwich to visit family, and on came the lambda light, but she was driving fine. When I got there I pulled number 1 fuse and left that overnight. Started the following morning and much to my annoyance the light came back on after a few hundred yards. Pulled fuse over Sunday night and the light came back after a mile.

Now here is the funny thing. The 100 (nearly) miles back, A120, A12, M25, A2 A289 A228 were mostly done at 70 mph apart from bits of road up on the A12 whch were 50 - and when I filled up I had done almost 39 MPG. I would have expected 25, maybe 27. So possibly I am running very lean although she is going very well - although slower than my other Sport and maybe a bit later for the turboplus to kick in. I used a bit of oil (well, she has 214k miles) but no water.

So, the optimal diagnostic process...

I have five (I think) AMMs in the garage but no air filters. Safi's garage 100 yards down the road has all the MoT gear to assess exhaust gases and lambda. And I have been thinking for some months it would be good to do plugs, plug leads, distributor cap rotor arm and filters and maybe coil - ie a full stage 0.

So I think I will first ask Safi to do a pretend Mot just on gases and Lambda. If that shows the lambda to be correct then I can ignore the light until MoT time. Who knows if the lambda light being on but the lambda being correct is a fail or not?

Second I think I will try all my AMMs to see if she likes any of them! If she does not, then the stage 0.

If the stage 0 and the AMM do not cure the lambda light, and the lambda is actually out of spec, what else might it be? And what is the optimum route to fixing it. I do not really want to replace the ECU.

I did build a flash tester a few years back, but have forgotten how to use it. Can somebody point me at the instructions and a list of codes?