blk92ES300

Hi first time poster and i wish it would have been another topic, but oh well. My 92 es 300 failed the smog test. It has 148k miles. it passed HC, CO, and NO at 25MPH at 15MPH it passed HC, CO, but failed NO by a lot max was 767 and i got 1533. I did run the test with fuel injector cleaner dont know if that hurt? But since it failed i changed the plugs, wires, cap, rotor, and oil/filter then i took the car back and the guy said that it didnt look like i was going to pass and i i wanted to abort the test and save my free retest. So now that ive done those things what could be the prob and fix?

oh yeah i forgot to mention that i put a vacum hose to the egr valve to test it and the engine stuterd. which i heard means its working?

anyways thanks for any help you guys can provide and i enjoy the site.