Just read data from my car.

Short term fuel trim b1s2 is constantly at -100% and stft b1s1 seems to be fluctuating from anywhere between -5% all the up to 45 %.

I don’t have any error codes but mpg is very poor.

Any idea on the steps to take to find out the issue?

It’s a horrible Renault scenic II 2004 1.6 petrol

french cars suck, period. I would assume computer or other electronic failure with those nutty readings, if it was mechanical thing couldn't run at all with such drastic swings

It’s now got a P0010 fault code. Possible camshaft sensor? Or the vvt solenoid?