Hello, I have a 2007 fiesta zetec s 1.6 petrol and have been wondering about the o2 sensor readi gs on my car. 

At warm idle the o2 sensor 1 fluctuates between 0.1 and 0.9 volts but it does this very slowly. It will go too 0.1v then back up too around 0.85v and stay there for around 3 or 4 seconds and then go back down. 

The Internet seems too suggest that it should cylce rich too lean every second but mine does it a lot slower than that maybe every 3-4 seconds

The sensor 2 is reading a steady voltage of around 0.85 at idle and doesn't fluctuate so I know the catalytic converter is good. 

Does the sensor 1 seem to be failing? 

Cheers for any help 

I think the old saying "if it's not broke, don't fix it" applies here.

Is it actually causing running issues or throwing a code? Don't worry about it if not.

3 hours ago, Luke4efc said:

I think the old saying "if it's not broke, don't fix it" applies here.

Is it actually causing running issues or throwing a code? Don't worry about it if not.

Hello mate, there are no codes or anything. The idle seems a tiny bit lumpy sometimes but other than that everything seems to be alrigh