Fieata CFi emissions

[cliftyhanger]

My delightful sister has a 1993 Fiesta CFi thingy. It is actually pretty good, but failed the MoT on emissions. A good thrash (first one for a year) got them down a lot, but still nowhere near a pass. MoT man (ex pupil who I got on with, so no bull) reckoned the cat was the most likely suspect and not expensive. So, new cat, new lambda sensor all fitted, and still fails when big sis takes it back to be checked. The lanbda readings were too high at the fast idle test.
So, anybody got any bright ideas? I am running out of them, but I am guessing testing the air temp sensor (how do I test it?? and get a spanner on it????) or coolent temp sensor may be next place to look?
Any help oh wise ones?

[mk2 24v]

if its the lambda reading thats too high, check for any air leaks in the exhaust system and the inlet manifold as well

had plenty of iffy lambda readings cured with pin holes in the exhaust sorted