High CO2 emissions on Mot

[manity]

Hi all could anyone help with an emissions question..

i have a 2004 1.4 polo it recently failed its MOT ( natural idle CO = 0.40 pass .... second idle CO = 0.42 fail and fast idle CO 0.44 fail).

i changed the air filter and plugs added some injector cleaner and took it for a 20 mile run in 3 ( automatic). its wifes car and only does around town driving about 10 miles a day max so expected it was a bit clogged up.

as a result 2nd MOT reading were a close pass ( natural idle CO = 0.32 pass ... second idle CO = 0.30 pass and fast idle CO 0.34 fail).

i have checked there are no fault codes and although it passed just. the readings still seem high ( what should they be? average).

ive included a screen shot of MOT results as a pic.

any help would be great thanks.

Edited by manity on Friday 12th April 17:39

[GreenV8S]

It's not CO2, it's CO.

CO is the result of incomplete combustion, typically a symptom of running slightly rich. The slightly high HC figure and low lambda figure are all consistent with the theory that it is running rich.

[manity]

Hi thanks for the correction. any ideas on what might be causing it to run rich. i saw on another forum someone had the same problem and they changed the Cat and the CO dropped from 0.5 to 0.01 overnight. thinking as i have no fault codes showing this might be the case with mine.

[E-bmw]

Fault codes aren't the be-all-&-end-all of engine health.

I would recommend doing a full service on the car complete with engine oil & filter & breather clean/replace, you will likely find that will help somewhat.

[Coilspring]

manity said:

Hi thanks for the correction. any ideas on what might be causing it to run rich. i saw on another forum someone had the same problem and they changed the Cat and the CO dropped from 0.5 to 0.01 overnight. thinking as i have no fault codes showing this might be the case with mine.

Before going to that expense, try changing the air filter and see what difference it makes, or not.

[GreenV8S]

I agree with the suggestion of the air filter. If that doesn't fix it, also clean the area around the throttle plate. If it hasn't been serviced recently that's quite likely all it needs.

[manity]

hi thanks for the replies. i did change the air filter and plugs and gave it an italian tune up which dropped the co just enough to pass the MOT.

[E-bmw]

As above, now do oil & filter & check/clean/replace your engine breather.