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HELP 182 keeps failing MOT emissions test



I really hope you guys can help me with this, because the garage are telling me they are all out of ideas and to take the car to a specialist. I've already spent £800 fixing all the other MOT problems and can't justify spending much more on this car.

It's an 04 182 on 105k miles. It failed the emission test with the CO levels being too high: Fast idle 0.82% (limit 0.20%), Second fast idle: 0.74%, Natural idle passed at 0.26% (limit 0.30%). Everything else was a pass. I can post the data too if that helps?

2 months ago a 200 cell sport cat was fitted with a new centre silencer (powerflow). It has existing Miltek rear silencers. When it failed the MOT emissions they said it looked as if the cat was to blame, so with it still being in warranty I took it back and they fitted a 400 cell cat. This didn't make any difference to the emissions readings.

Since then a new lambda sensor has been fitted because it was throwing up a fault code (again making no difference to the emissions) and it has had an oil change. They say that two pistons have low compression. I don't know how low, but it hasn't been burning a lot of oil. It will gradually drop down over a few months.

The car is standard other than the exhaust. Standard airbox. The acoustic valve has been disconnected if that makes any difference. They also tried fitting a new MAF sensor, which didn't help the readings either.

Is there anything else obvious that could cause this?
 
  dan's cast offs.
tell them to take their time doing the fast idle, there is no time limit to get the co down before they start the actual test.
 
  BG Clio 182
It will fail like that if the temp is not coming up all the way. If your gauge is not sitting at the dead center line replace the temp sensor and thermostat and you should be good to go.
 
Well it turned out to be the cat. Despite having two new sport cats. The garage tried a pattern part cat and it flew through no problem. The garage who did the exhaust paid for the pattern cat and fitted it.
 


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