Emission test fail high NOX

[JBRGUITAR]

Greetings all,
This is my first post as a new member of TN and I hope you can help me out.
I have a 03 matrix XR with about 200,000 KM (130,00 miles) . 2 Years ago I just barely past the Nox and this time I failed. The reading was 2014 with the limit being 505. The Hydro Carbons and CO passed no problem.
I read a previous post from someone that had an 04 and all that was suggested was a throttle body cleaning, change plugs and PCV valve. I went to the local Toyota dealer and a mechanic as well as a veteran parts person said they hardly ever replace PCV valves. The mechanic also thought that it was probably running lean thus causing the engine to be too hot. (Does running lean mean it is getting too much fuel due to a shortage of air?)
I took it to a Canadian Tire (the toyota dealer didn't have a Dyno) and the mechanic said it needed a new O2 sensor (the top one), The toyota part was $283. That at 3000 RPM it was showing lean. He didn't guarantee that that would solve the problem.

So... Your thoughts would be appreciated on an alternative solution and on where a cheaper parts source would be. Thanks folks

Bruce from Bowmanville , Ontario Canada

[mistamatrix]

That's a pretty high failure. I'd hold up on an O2 sensor replacement if you're not getting any CEL's. Running lean means more air/less fuel. What kinda gas you been using? I'd try Sunoco 94 on the next tank before a retest.

[JBRGUITAR]

I have been using regular gas always. If I use Ultra 94 and it passes then does that suggest what might be the solution? There are no CEL's (i assume that means check engine light) and the car runs , starts great.

[fishexpo101]

High NOx levels are a sign of too high of a combustion temperature - car is running too lean, not enough fuel to help cool down the resulting mix. Could be too much advance on timing, hot spots in engine, vacuum leaks.

The suggestion for high octane is a pretty decent test. High octane resists detonation, which could be generated by hots spots in the engine, or excessive combustion deposits that are effectively raising your compression ratios.

Do you have more information on the test - was the high NOx on acceleration, idle, etc.?

[JBRGUITAR]

The high nox was at 3000 rpm. I don't know if I mentioned that the car runs great.

[mistamatrix]

update?