well the only mods that i have done to this car is a pte 93 octane, chip, rjc boost controller,i put a new cat on it too. HC standards in chicago for a 87 gn is 2.00 i came in at 2.63 everything else it passed. .i dont know what to do the car is stock everywhere else and i dont have the stock chip .are gns supposed to run like they have a slight miss i put a autozone coil pack and module on too 2 yrs ago and i have a new ac delco 02 sensor. after i failed i used some gm top engine cleaner i havent gone back to retest it yet .