emissions fail on b4

Hello lads any help here would be great. I have my 99 leggy in for three tests now and she passes on everything but emissions. I have the factory exhaust and downpipe back on her for the test. Lambda is below the 97 at 94 and th CO levels are at 2.3% well above the 0.30% level. I replaced the lambda with a second hand one one and hasn't made a difference. Just not to sure where to go I know that it will cost a bit to rectify but I want to make sure I spend in the right areas. Hoping someone can help thanks.

Have you checked the second hand air fuel sensor is actually working?

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have you checked the MAF sensor as well as the intake piping all the way up to the manifold for leaks? Air escaping in our leaking out could throw off your readings as well.

Emissions fail

I did a small smoke test on the intake side and it seemed fine however I did notice a small leak over by the boost solenoid would that throw the reading off?