For high NOX I suggest you look at your timing, EGR valve, catalytic convertor, and fuel mixture.

Your timing is way off for your altitude. As mentioned before, it should be 7-degrees BTDC +/- 2-degrees with idle set to 800 +/- 100 RPM (see note below). Use SAS-1 to adjust your idle.



Regardless of what the mechanic said about adjusting it possibly making it worse, if you can't get it to run right with the timing set where it should be then something else is wrong and not setting it correctly won't help in finding the problem. Of course, if you can't set it correctly then something else is definitely wrong.

The EGR valve can often get gummed-up with carbon. Cleaning your EGR valve is easy to do.

Your rough idle when cold is probably due to your choke not set correctly. Just make sure when you go take your emissions test again that the engine is plenty well warmed up. Take it for a good half-hour drive right before you go test it.

If your cat is the original one, it may be time to change it. If the head gasket has blown in the past (somewhat likely on a 2.6) then the cat may be getting plugged up, preventing it from scrubbing the exhaust properly.

If your fuel mixture is too lean your combustion will be too hot and may produce NOX. Fuel mixture is adjusted with the MAS adjuster (see image above). Clockwise = leaner, counterclockwise = richer.

*** NOTE: There are several adjuster screws on the carb and adjusting the wrong one can be bad as it is set at the factory and shouldn't be touched. If somebody in the past has monkeyed with SAS-2 it can be troublesome to get it set back right. In short, be careful which one you adjust. Don't mess with SAS-2. ***