Newbie posting.

I have had a 1995 Fiesta for a year. First big repair came this month - a replacement automatic choke (AA repair man's advice). Job done by my local dealership, on my instruction (i.e. they didn't do their own costly diagnostic) for £280.

I just had emission tests done today which put it well over the CO limits in all except natural idle. It passed MOT emissions last year and HC and Lambda are still fine.

I've read a few posts recommending additives to the fuel tank, and others recommending cleaning the lambda. I'd rather keep her on the road than go for scrappage, but don't want to own a money pit.

Could this be down to the choke being poorly installed? E.g. is there a high fuel:02 ratio now going into the engine? Can anyone explain the interdependencies between the choke and MAF or lambda or can anyone tell me where to find them so I can work out if the dealership buggered up the installation?

And anybody who can give ballpark estimates of the costs to put it right would be my legend of the week.