Car Failing its MOT

[measor]

Car has failed its MOT on emmisions as it is running to rich. I had decat pipe on for a while but put the cat back on for the MOT but it still failed. Now I know it can be a number of things which is making the car run to rich but does anyone know a common cause?

It could be my lamba sensor as I have an idle problem which is described somehwere on this site which sounds exactly the same.

The car was booked in for a full diagnosis but I cant afford to spend the £80 just to be told the problem as ive already spent about £1500 in the last 4 months on repairs.

What should I be checking?

Cheers

[Gav]

i had the same prob and was lambda sensor.

I had to have a new one put in and a new ISCV


u wont pass unless u take it to a tuner tbf...i had to do it, £80 for me also

and that was after i spent £thousands on it being restored

[measor]

Ok cool, why did you have to replace the ISCV as well? Is it worth buying the lamba sensor from somewhere like GSF or are the patent ones no good?
If i replaced the sensor would it still need to go to a tuners, what is it that they will do?
Cheers