Well good luck running 0.9 on idle, I guess you dont care about consumption at all. Yes its small amount to change but it will have an effect.
The fluctuation is really miniscule.
Man, setting lambda 0.9 is only for diagnostic and testing purpose and only in idle rpm range. I am not going to drive like that on a daily basic
I went even further and set to 0.8 and engine works even little bit better, almost without rpm drops/spikes which are correlated with engine load changes (rpm spike when load drops, rpm drop when load spikes).
The bigger issue than consumption is fouling the cat and getting soot on the spark plugs.
It can also never pass a MOT sniffer test.
No cat here
but situation was the same with and without cat.
Problem is now that with lambda under 1 engine runs open loop.
