'06 Yaris - 2nd NCT fail with emisssions

Sin1981

Hi,
I have a 2006 Yaris, (120k miles on clock). I had NCT 1 month ago, and had the following fail on emissions:

Low Idle:
CO 0.04% (limit is less than 0.30%) PASS
HC 86ppm (limit above 0) N/A

High Idle:
Lambda 0.93 (limit is between 0.97 and 1.03) FAIL
CO 1.92% (limit is less than 0.20%) FAIL
HC 702 ppm (limit above 200) FAIL

I was up in my home town and took it to a local mechanic. He looked at plugs, did oil change, and told me to remove the air filter prior to the Re-test. he also put some REdex in the tank, and told me to put a bit more in prior to the test, and give the car a good drive.
I followed his instrustions, (good drive being a 10 minute drive on the motorway, in the usual gears. I didn't drive in 3rd gear etc).

Unfortunately, the car failed again. results as follows:

Low Idle:
CO 0.02% (limit is less than 0.30%) PASS
HC 16ppm (limit above 0) N/A

High Idle:
Lambda 0.99 (limit is between 0.97 and 1.03) PASS
CO 0.57% (limit is less than 0.20%) FAIL
HC 30 ppm (limit above 200) PASS

I was really disappointed. Today, i took it to a different garage in Cork city. On looking at the NCT results sheets they said it pointed towards the Catalytic converter. anyhow, after doing some diagnostics, they came back and said there appeared to be no issues with the CAT, no issues with sensors, no faults coming up on the computer. He was a bit stumped and was surprised the emissions are high based on what they saw.
He suggested that I use Diphetane......... I'm kinda at a loss.
Is Diphetane the same as Redex. would revving the cards lots in a low gear have helped?
I could use the Diphetane options, but feel it's another shot in the dark, and it might fail again.
I did tell the mechanic today that it burns a lot of oil, and need new oil added 3 or 4 times per year. i don't notice smokiness...

Any thoughts/suggestions?
thanks!

rex-x

Its the cat, you killed it by running the car in the rich state it was in at the time of the first test

Leonard Hofstadter

It's still running slightly rich (the lambda value is less than 1) so that could be part of the reason it's failed, rich running will increase the CO emissions for sure. Although it's so close to optimal it seems a bit far fetched to think that's the reason it failed.

How much oil is it burning? Unless it's more than 1 litre per 1000 km or 600 miles it's not going to cause you to fail an emissions test. Most modern engines do burn a bit as they get older and many Toyotas are known for doing it. The fact you say you don't see anything is proof that it's not burning too much, if it was burning lots of oil you'd see blue smoke.

Sin1981

it is empty of oil 3/4 times per year. I wouldn't put huge mileage on it. approx 10k / year.