mk1 failed NO test

[deportes]

New to the forum, I hope I can help as well.
The plugs are whiteand supposedly running lean.
Checked the EGR valce and it is in good condition, the Actuator I need to check next.
Any other know culprits that make the car run lean.
Timing is perfect on the yellow mark, new plugs, higher octane gas. What elsa can I do before re-testing it?

[OEMonkey]

If you failed NOx, most likely the egr passages need cleaning. Testing the egr by applying vacuum to it while idling is not a good way of testing it. All it tells you is that it opens when enough vac is applied. Also check your base ignition timing, check for low fuel pressure, a rich biased o2s, vac leak, etc.
NOx forms when temps are high. High temp is caused by a lean condition.

[deportes]

Thanks OE Mokey, I did remove the EGR when I tested it and all passages are clear as well as the tubing to and from.
The timing is good, 10deg btdc.
How do you check for a rich biased O2s?

I willperform the other checks. I will also test the EGR actuator to see if it works as desired.

[powderblue91]

check your o2 sensor and if your car was built in 91 or later it can be your cat. converter

[deportes]

GOOD NEWS, it passed. Last time the NOx was 1135
max 825. Today it was 822 wow...
Put un new sparks, 91 octane fuel and prayed a lot. 2 more years.