My mpg seems have declined lately could be me foot or something else.Having the cat removed tommorow will see if that changes things.Otherwise Ive read somewhere the lambda sensor needs replacing routinely .Is it worth replacing as a matter of course?
No. These hardly ever fail. However, replacing it isn't expensive. If they go really bad the CEL (MIL) will illuminate anyway. I know Bosch ran an advertising campaign a few years back to promote routine changing out the O2 sensors but they stopped. Professional mechanics will advise not to bother unless it goes bad. I changed one on my very high mileage 86 9000T and it made no difference whatsoever.