Cant pass smog with 90 GTU
 

Im having a heck of a time trying to get my STOCK 90 GTU to pass smog. I just dont understand it, its completely stock. It idles better then my other 2 rx7's (89 GTUS, 90 Turbo), any ideas as to what could cause it not to pass? It has 161,000 miles on the original motor, catalytic converter has only got 75,000 miles on it, new spark plugs. Any ideas guys, i really need help as im trying to sale the beast.

Replace cat!!!!!,Cat on are cars take a beating. With that many miles on it, it shound be replaced, Also check abv valve next to your smog pump it controls fresh air to your cat!!!