NCT emmisions testing machines

Hi everyone,

I recently put my car in for an NCT after getting a pre nct on it, it came back with high emmision levels so I brought it back to the garage where I bought it and they took it back and and put a treatment into it and also fit a new lambda sensor, they then put it onto their machine and the levels came down. So back up to the nct and the same thing again emmisions are too high, back to the garage and the guy fitted a new catalytic sensor on and it was fine again, back to the nct and it failed again. The guy in the garage didn't know what to do so he told me to go to a renault garage so they could put it on a renault machine and check everything was ok (it's a renault clio).

Brought it to Renault this morning and was waiting to hear what it could be and how much it was going to cost when the guy rings and says he has all the print outs from the Renault machine and there is absolutly nothing wrong with the car or the emmisions, he said he has had a couple of people coming to him with this problem and so he has printed out the results from his machine and they get passed, they basically think the nct testers are not giving the machines enough of a break in between the cars so the wrong reading is coming up.
I'm just wondering has this happened to anybody else? Did they pass when you went back up with the results??

Had my car NCT'd last week (it's a 00 plate, so not new). No problem with emissions. Can you verify if the emission measuring for all the tests you had was the same?
Or did it actually come down from the first one?
Also, what is the difference in readings between NCT machines and yr garage?

We didn't have this problem but our garage mechanic did mention something similar to me.

I also spoke to someone a while ago who had a problem with the NCT centre that they were going to. Not emissions problem but they were toing and froing between their main dealer and the test centre and had come to the end of their tether. According to them they changed to a different centre for the retest and it passed straight away. Worth considering.