Your Toyota Corolla's high NOx problem could be caused due to a lean fuel condition and/or a defective EGR valve (if equipped). if you've made sure these two things are not the high NO culprit, and you've verified engine cylinder compression is high due to carbon build-up, go ahead with an engine decarbonization.
You can use Sea Foam to help with removing carbon build up from your 1992 Toyota Corolla's valve heads and pistons, but depending on how bad your vehicle failed for high NO, Sea Foam may or may not help. Smog check repair stations have a more heavy duty product they use which is mixed with water and administered through your Toyota's intake manifold at 2500RPM. But again, how much this will help your Toyota Corolla pass the smog check will be unknown until after you use perform the engine decarbonization.
Removing carbon from your Toyota Corolla engine will reduce cylinder compression, resulting in lowered NO emissions. We recommend performing a complete diagnosis of the NO failure including all emissions components prior to performing the decarbonization due to the fact the carbon removal process, especially one which is administered through the intake manifold while your Toyota Corolla's engine is running, is very hard on your engine and can potentially cause more damage then good if not conducted properly. Engine decarbonizers, except for those products which are poured in through the gas tank, are always used at the vehicle owners own risk. See product usage description for proper use.
