Lambda mot car refuses to pass test

[gullpayne]

Hello guys hopefully someone can help me,
i m in aberdeen,
Have 3 fails on Mot for emissions,

first was for high lambda with co2 and hc fine, got new exaust box fitted,

next fail was for high co2 with lambda and hc fine, two bottles of cataclean sorted that out,

went back and then lambda failed again,

first test was in kwick fit and they could nt fix the lambda problem,

next test was at council and they could nt fix the high co2, said get a new cat, but cataclean seems to have sorted high co2,

then went to peter vardy today and the car failed on lambda again,

I also got a new lambda sesnor fitted two days ago, I drove around like mad before the test today and it still failed on lambda after passing in a previous test, like 2 weeks ago,

is this a common problem? fail co2 and pass lambda in one place and pass co2 but fail lambda in another place,

car is a 1998 audi a3, brought it to local mechanic as i trust him, he said change spark plugs might do it,

only problem is I have to keep paying for test after test and re test, i ve got a diagnostic in kwick fit they said was fine, and another diagnostic in nivlem, they could nt identify any problems either, both these cost £100 and £35 respectivly, i dont want to go to Audi and have them do a £90 diagnostic to tell me I need a new lambda sensor after I ve just fitted one, got one from ebay for £17, audi charge £100 for a new sensor, excluding labour,

I m only a poor student so cant afford these prices so I m forced to seek other methods which thus far have proved futile,

Thanks for any responces

[zollaf]

what values are you getting on lambda ? is it high or low , can you post up the fails so we know what we are dealing with ?

[gullpayne]

|Lambda 1.20 on idle 1 and idle 2
co2 0.228, on 1st and 0.024 on 2nd
hc 92 on first and 35 on second
just had spark plugs changed and computer diagnostic no faults, will take for emissions test before mot re test, mechanics are baffalled, said might need new airflow meter,
Thanks for the reply

[zollaf]

i would say its been rushed on the test and the cat just wasn't hot enough. it needs to be properly hot when tested and not allowed to cool down after a run.

[Drifterwanab]

My g/s has just failed on Emisions also. Garage said lambda readings where way high

I pluged it into vag come and it is saying precat lambda is faulty.

Sorry to thread hijack, can some one advise me how i read the values real time and what they should be?
Also any one got a used lambda going cheap northwest area its 2000 1.6

Ta

[zollaf]

my g/f has pretty bad emissions also, but thats another story altogether.
anyway, is your computer telling you that the lambda is goosed or that it has picked up a fault. the lambda sensor measures oxygen in the exhaust, as does the mot test. it then relays this info to the ecu so it can adjust the fuelling to keep it as close to 14.7:1 as possible. if you have say an airleak, then there will be too much oxygen in the exhaust which the lambda will pick up as a fault and the ecu will try to correct. a slight blow in the exhaust can also cause similar problems. a lot of lambda sensors get replaced , both by diy mechanics and by professionals, usually when people rely too much on a computer and don't really know what they are doing. the thing is, to test one properly you really need a scope which not a lot of people have . what were the mot reading though , as a lot can be gleaned from those.

[Crasher]

Used lambda probes make as much sense as used spark plugs!

[Eshrules]

I will never understand the logic behind fitting second hand consumables, Lambdas are what, £50 ish?

[Drifterwanab]

Well my logic was the only ones in europarts are £200. And to spend £200 on something to find out it wasnt that is madness on £1000 car

[zollaf]

this is where experience counts. what fault code are you getting ?