Arghh! some one help me please! I've got a 1.1 mk3 fiesta with a 1.8 zetec in it. Put it in for an mot - failed on many things including the exhaust blowing. fixed all problems but when emissions were tested it failed (quite badly) on the lamda when on idle. Everything else passed. Because i've had the exhaust fixed it can't be that and i don't think the cat is blocked. Have taken air filter and inlet off and cleaned with petrol based cleaner. Anyone got any idea what the problem is? I bought the car with the conversion done so don't know too much about it?

any help appreciated