Using more petrol? Unknown reason :( Options

[Liam_c]

Hey everyone

Lately my car has been using more petrol than what it usually would, and i have no idea why.

When i bought the car, i was running it on 91 octane, and it was using about 8.5 L per 100km, and then about 2 months ago i upgraded to 95 octane and it was using 8.1L per 100km. No mater how i drove it on 95, it was doing high kms every tank i was loving it

But recently, its jumped back up to 8.5L per 100kms, and even though im driving it nicely, its still using alot of petrol. I started to notice it shortly after i had taken it on a car club run about a month ago ( driving around the hills, giving it a bit of stonk in the hills)

To some of you, this may not really be a problem, but its worrying me as i don't want it to get worse (and on my current run, it seems to be getting worse )

Where would be a good place to start looking for what could be causing this issue? I'm 90% sure it isn't a leak, as there is no noticeable marks on the ground after being parked up.

Air filter? Catalytic converter? Wrong fuel type? Fuel filter? O2 sensor?

Thanks

Engines a 3sfe.

[RabidTRD]

Your upstream O2 sensor is what controls fuel trim. If it hasn't been replaced, look at that at the same time as the tune-up.