It sounds like the mixture could be too lean. One question I have is a year ago I had a high idle problem. A mechanic replaced leaky vacuum hose and the auxillary air valve. It still ran high idle when it was cold. Someone on the forum suggested tapping the center of the Aux. air valve. I did this and the high idle stopped. Now since I'm having a problem with high NO measurement could tapping on the A. A. Valve have effected the mixture so the engine runs leaner?