Ok guys.

These are the symptoms on my car today.Looking to confirm if they are similar to the symptoms of a faulty O2 sensor :

1 When engine is cold, idling a little rough (almost
unnoticeable).The drive is normal.

2 When warm, idling is very rough.Hesitation from standstill.Drive
is very rough (engine idles roughly).

3 Degrading fuel mileage.2 weeks ago, i could get 450km+ on a
full tank.Now i can only get 260km.

4 Exhaust smell is stronger, and exhaust note seems louder;like
the car is running rich.

Your quick opinions, please.

Thanks in advance to everyone!