Having an aftermarket intake manifold on your Honda Del Sol should not cause high NOx... but we can not rule it out. If your Honda's high NOx is due to a lean fuel condition it might be possible that the aftermarket intake unit is allowing more air to enter the combustion chambers than the ECU (engine control unit) is programmed to allow, as well as the MAF (mass air flow sensor) calibrated to measure.
If you have the original air intake unit we'd recommend installing it, driving your Del Sol for a week or two (for the ECU to learn new fuel trims) and than get a smog check re-test. Good luck.
Joe - SmogTips Support
posted by SmogTips Support