90 LS400 NOx Emission Failure - Happy Ending

My state limit for NOx was 875PPM... The car FAILED with 975PPM... Strangely enough, the HC and CO were WELL BELOW the limits and I never experienced and Engine Check Light activity.

The EGR valve is attached to the manifold with a little "adapter" which directs the output of the EGR value through a (cooling?) channel before directing into the engine (manifold). That channel was (almost?) completely blocked with rock hard black carbon. Using a dremmel tool to grind it out and a shop Vac to suck out any loose debris, THEN cleaning the EGR valve (and vacuum modulator/filter ) with a little carburetor spray ... and I was back in business! Retested at 717PPM. My highway MPG has always been ~25MPG, but my local MPG was pathetic ... The local MPG seems(?) to be much better now and Highway is getting ~26MPG. The car NOW idles at higher RPM until warmed up.

230K j
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Jerohm
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