1987 Toyota Cressida 160,000 miles failed high NO at 4000 ppm. Why?

Cressida failed the smog test 4 times last month. This car never failed smog in the past, but I let it sit for a year. When the car was on the roller, it was pinging and failed for high NOx (~900) and distributor was off 7 degrees. I brought it back with the correct 10 degree distributor adjustment and it failed NOx at (~2000) and the pinging was still there.

Had a tune up done to it including new plugs, wires, air filter, oxygen sensor took it for a 400 mile drive with fresh new gas. Took the car back and it failed NOx (~4000) and has a slight misfire and the typical strong odor from the tailpipe. At this point, I'm stumped.

Answer:		Carbon build-up! That's our guess at this point. Do a compression test. You will probably see compression upwards of 160 to 200... Way to high. You may want to perform an engine decarbonization with some Sea Foam. The Sea Foam to help with removing carbon build up from your Toyota Cressida's valve heads and pistons. Removing carbon from Toyota's engine will reduce cylinder compression, resulting in lowered NO emissions. Just remember the carbon removal process, especially one which is administered through the intake manifold while your Toyota is running, is very hard on your engine and can potentially cause more damage then good. Engine decarbonizers, except for those products which are poured in through the gas tank, are always used at the vehicle owners own risk. posted by SmogTips Support