Failed NCT on emissions

Iceman29

Hi guys
Just back from the second NCT.... Failed two weeks ago on low idle getting a reading of. 33%. Put dipetane in last night and drove it around and today got a reading of. 55%....how is that possible? Any advice?

ongarite

What car? Engine type, size? Year?
High idle, low idle and lambda values?

Iceman29

ongarite wrote: »

What car? Engine type, size? Year?
High idle, low idle and lambda values?

Sorry it's a
09 golf.1.4 petrol
It fail on the high idle below
High idle 2800rpm
Lambda 1.03
Co. 55% Vol
HC 211ppm

Low idle 780%
CO 0.15%
HC 15 ppm

ongarite

When was the car serviced last as the lambda value is right in the failure limit..
When was air filter and spark plugs last changed?

Iceman29

ongarite wrote: »

When was the car serviced last as the lambda value is right in the failure limit..
When was air filter and spark plugs last changed?

Serviced about a year ago I think. The results two weeks ago were as follows....dunno how there is such a huge difference after adding the dipetane

High idle 2700rpm
Lambda 1.01
CO 0.33%
HC 163

Iceman29

What would you guys think? Maybe I didn't drive it enough to get the dipetane through?what happens if you fail a 3rd time?

jimgoose

My somewhat educated guess would be a failed/failing cat-converter.

You'll need to get it diagnosed somewhere. The lambda value indicates that the fuel injection system is not able to keep the mixture at lambda 1.00 but it's running lean instead. Possibly a failing vacuum hose or other leak, tired lambda sensor or some other sensor. Cat itself most likely is fine as it's not much over even with fueling being out.

Iceman29

Thanks guys, would you think the dipetane is worth a try?