Ok. When you test a car in second instead of third the NOx will be higher… higher RPM resulting in higher cylinder temperature. 91 octane does burn hotter but if you test it in second gear with 87 octane it may start pinging… depending on the setup. Pinging will make high NOx readings too.
BTW the test could have been done properly. because at the time of the test the RPM could have been unstable in second gear resulting in having to test in 3rd. You could always try to get a test out of them… or test it somewhere else and send in a complaint about the place that tested it in third.
Also the egr valve isn’t the only thing that controls NOx. There is many different things. Coolant temp, Bad MAF (lean), Bad O2, Vacuum leak, Bad Cat, Improper timing.
Since the NOx arent really that bad, I would make sure basic things are good. Ie. Make sure that there is no check engine light on, that there is proper coolant flow (all hoses hot and thermostat open) Get the Cat hot. If you did all that. Turn the heat on full blast (tell the guy testing it to leave it alone)
Try retarding your timing if you have a distributor, I found this works very well.
Yes testing it cold will work too, but that is frowned upon because it goes against the SOP and chances are if you don’t know the person they wont do it. They dont have to test it cold just because you say it. They also don’t have to test it again for free because someone thinks they did the test wrong. A bad tach connection could also be the reason why that number is so low.
But you could always try.