When car next in for it's 12month service going to get both sensors replaced, one I know is not actually doing much from the error code I got from my local car tuners, he thought they were dodgy just from listening to the idle, which is quite lumpy and bubbly, it was showing as running lean. I believe this means it will be fooling the ecu into making wrong adjustments. So am hoping it will be running even better and faster when done ? This is why if I leave it idling for too long the engine light comes on.

" P1131 lack of H02511 switch-sens lean"

Have you tried cleaning the sensors, maybe worth a try

Quite easy to do to get them out if you have the tool

I don't have the tool nor the inclination to jack the car up and get under it these days, I'd guess these are really tight as well, best left for garage I think, the tuning guy showed me the live readings on his lap top and he said the sensor wasn't actually doing much.

fair enough mate