On my way to the roadworthy (MOT) the yellow light came on with reduced engine performance. Booted it and it seemed to go away. Came back on on the motorway and went off again..anyway it passed the emissions and got a test certificate.
No DTCs on the i930. Have just done a hard reset and moved the throttle back and forth a couple of times.
Will set off for a test drive with scanner attached and hope I can stop if the light comes on.

Any advice welcome .
ADDENDUM
Just been out and light came on after about a mile and went off straight away ...reader says no codes.
Ran fine another couple of miles and at idle there was a stumbling misfire so need to take the coil covers off and get the stethoscope out .....

 

SORTED.
Well with the computer giving me no help we must revert back to the old ways...
Its got a rhythmical miss so as an engine only needs air fuel and spark which is it ?
The TPS on the Scangauge is showing normal and then I remembered when I had it I investigated what sort of timing chain tensioners it had had fitted at 77000 miles and found oil in one of the plug wells.
So off with the coil cover on the RH bank ,out with No 3 and blew it out with compressed air and got some mix of oil and water....Replaced the plug and fitted my second-hand spare coil and its sorted.
In retrospect, the car was often reluctant to accelerate so must have gone into some limp mode but not put it on the dash..goes like **** off a shovel now at all speeds.
Plug was *** ash grey so all good from a mixture point of view ..doing 33MPG UK on my last cruise to france.
so no complaints there .....

 

A lot of codes (by law) need to have a situation occur at least twice in succession under quite similar circumstances, but the car's computer (PCM aka ECM) may have to defend the engine before the second (or first) time. That's where I think you were at.

Good news you fixed it.

 

Was aware of that and thanks for your interest.
Due to bad repairs to the coil cover holding inserts the cover is not 100% sealed. I think someone washed the engine prior to purchase and let the water in ...another job!