ok people, my exams are over and ive got time to solve this super annoying problem. my car sailed thru MOT (aside from a knackered shock) passed emissions tests as well. but i still get terrible fuel economy (in the 20's) driving sensibly in town. i have replaced lambda, but dont know how to test if its any good (i went for the cheapest i could find) HT leads and sparks are recent. and has a new HG. so realy am stumped would love some input!!!!

I assume you keep your tires inflated to recommended pressure, and have car serviced regular, if so then you want to be checking things such as lambda, exhaust system is another culprit sometimes, lambda sensor is best checked with ociliscope as it is very fast switching, between 0 and 1 volt, 0.5being lambda =1, also check air temp sensor as it puts more fuel in when cold, cant remember the way to check this, as it is a while since i have done it, also check coolant temp sensor, you will need a multimeter for this, i will post instructions later if i find them

ace, where are the air temp sensor and water temp sensor? i have an analogue multimeter that will tell me voltage change in lambda, what am i looking for and what is bad? could CAT be at fault? or would a broken cat have failed emissions? and yes tyres ar at 32 and 30 front and rear respectively. serviced fully less than 3k ago. HT's and sparks are recent. oil is good colour. enigine sounds fine, drives fine, and revs happily.