1.6 here, but your figures seem about right, im only getting an average of 32, on 'combined' cycle. variables are too large, what speed you do, any hills, what weight you have, driving style, even down to which oil you are using.
ive had as high as 42 and as low as 27...
why would you want to use cataclean to attempt to rectify a percieved fault with fuel usage?
best thing you can do is have a look at your fuel trim figures before you decide to condemn a cat but youll need OBD stuff to find out.
depending on how your lambda failed and how long it has failed for its possible you could have physically damaged your cat.
start with basics first, look into giving her a service if it hasnt been done recently (including air filter and plugs) and also see how your ecu is trimming the fuel.
