High CO, everything else OK 1999 1.6 s40
 

Hi Everyone,
My 1999 1.6 s40 saloon's CO is stubbornly high >2%..
It's just run in really (155000 miles) and is fine otherwise. No codes with a standard reader, temp sensor replaced recently.

Original exhaust/cat, oil is ok but will change. The plugs are a bit old and probably need changing and I would buy a new aircleaner element for the next MOT, but all that will probably only have a marginal effect, I am thinking..

My main candidate for the cause is a slight leak between exhaust manifold and cat which is making it over fuel...but I have been wrong before... I could not find an obvious leak, but the downpipe is not very accessible, of course.
I know the downpipe is a sort of double pipe arrangement with 8 bolts securing it to the manifold.

Other possibilities include the cat, but they usually are OK and I have been recommended 'cataclean' but I am a bit sceptical about that.

Anyone else had this issue with an s40 this old and how did you sort it?
Thanks,
Mike

correction
 

its six bolts on the manifold-to-downpipe..

If you have upstream and downstream oxygen sensors, it's probably time to replace them. Fix the exhaust leak you may have, change spark plugs and coils and see the changes.

O2 sensors
 

yes, I wondered about the O2 sensor, not sure there are two, will have to look..I was assuming it/they would be OK as there was no code thrown out, but I guess they could be a problem with out a code... they are not that expensive now..a cat is about 50 quid and the car is old enough to order one and fit it myself..