P0420 fault code

[Siimot]

Car keeps chucking up the above fault code - catalyst efficiency below threshold bank 1.
A previous had fitted a different cat could this be causing the fault code? The car does not petrol on idle, also seems to be struggling when cold to accelerate, a new lambda sensor fixed this a a while back but it's returning I think

Thanks

 

[RS Charlie]

Pattern cats can cause a host of issues. However, many people run without cats on here without an issue bar the odd error code, so I would doubt it is the potentially the cause of your issue.

How do you mean that the car petrols on idle?

 

[Siimot]

Thanks for the reply, sorry that should of said the car smells of petrol on idle and when you accelerate hard.
It had a lambda sensor replaced last year as it wouldn't rev over 2k when cold, that fixed the issue but it seems to be coming back again.