| You are obviously running rich down low. I have no explanation for the high NOx at low speed. Usually if you are rich, the temps are lower and NOx typically has a direct relationship with temperatures. High temps cause high NOx. I work in the environmental field. I used to be a stack tester (measuring emissions from heavy industrial smoke stacks). I have also struggled with passing smog (here in Ontario Canada). In the past I have hooked up my own monitoring equipment to my Z and made the necessary adjustments to pass. Many ppl have managed to pass the strict Ontario smog requirements with NO CATS. The techs are usually too lazy to do a visual check, but honestly, with no cats (unless you really know what you're doing) you're gonna fail so they don't bother looking under the vehicle. Anyhow, a vacuum leak at the plenum should lean you out a bit at lower speeds when the engine is pulling vacuum. This should bring your HC #'s down. Might not help your NOx though. I'd jump straight to the methanol fuel mix. Worked wonders for me. As I said, many people run a methanol mix with no cats and pass. Run your tank dry to get rid of that old fuel. Try a 80/20 fuel / methanol mix. 1 gallon jug of Methyl Hydrate (Hardware store paint section) mixed with 15 litres of pump gas. Mix it up and add it to your empty tank before heading to the testing station. Fill up with an ethanol free fuel as soon as you're done. Methanol is corrosive. You don't want it sitting in your tank for too long. Similar to ethanol it will also dry up rubber hoses, seals and O-rings. Fine for a quick trip for an E-Test in my opinion. Your idle might be a bit rough for the test but you should definitely pass. Of course everyone is going to suggest you 'FIX THE PROBLEM' rather than find a work around. This is preferable, but that'll take time and money all while those late fees are stacking up. If it were me. I'd get it passed and fix the issue at your leisure.
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