Oxygen Sensor location on 4.5L 'Cruiser

Fuel consumption has been slowly increasing over the past 12 months. I drive the same route every day and fill up at the same Shell servo. Used to get 300km on 45L. Now only get around 270km. Had a mechanic check it out and he replaced fuel and air filters which didn't fix it. I have read on the net that a crook O2 sensor can cause this problem but most mechanics change it without testing it first. Thought I would test it myself before forking out $150+ for something I might not need.

I think you'll find it in the exhaust system

Looked from the exhaust manifold down to the tail pipe, couldn't find anything with a wire on it. I haven't removed the heat shields on the manifold to see under it, but a can't see any wires leading from it so I don't think it's there. Besides, the "Cruiser has a split manifold that merges into one exhaust pipe so I would expect the sensor to be after the branch so as only one sensor would be required.

I told fibs here...this is the Airflow Meter, the O2 sensor is on the inner guard just near the windscreen washer bottle.

Hi Phil,
You seem to know a bit about Cruisers. I have almost rectified my Cruiser's drinking problem. I disconnected the battery for a few minutes to allow the ECU to reset itself. I'm almost back to normal fuel consumption and it's more responsive. I'm guessing the knock sensors had severely retarded the timing. (little tip for everyone). However, the idle speed is too high (820 rpm) due to the mechanic adjusting idle without first resetting ECU.I think idle should be about 650rpm. I cannot find an idle adjustment screw anywhere. Do you know if idle can be adjusted without the use of computers? 2000 model 1FZ-FE. Also, I can't find a MAF sensor on the beast either. On my friends 80 it's on the air intake, but not present on the 100. Thanks.

Can take up to 5 tanks of premium for the computer to reset its self on some vehicles, not sure about 4.5 though
Cheers Pete