CA SMOG Check failed
 

CA SMOG Check failed -- suggestion welcome


So I get the dreaded SMOG test thing in the mail and since I had a very hard time last time

here is what i did

1) added techron Fuel injector cleaner to full tank of gas
ran it to almost empty

2) after that I did go for an oil change

drove for about 15 miles on free way on 4th gear and got into the smog test station(Star certified)

First attempt -- Fail

15 miles
HC MAX 85 MEAS 88
CO MAX 0.34 MEAS 0.42
NO MAX 486 MEAS 871

25 miles
HC MAX 35 MEAS 35
CO MAX 0.30 MEAS 0.30
NO MAX 502 MEAS 312

Basically I failed at 15 miles and passed at 25 miles

Second Attempt Fail
3 gallons with a quart of denatured alcohol
replaced airfilter
Drove on free way for abut 15 miles and straight to a smog station


15 miles
HC MAX 85 MEAS 145
CO MAX 0.34 MEAS 0.56
NO MAX 486 MEAS 1144

25 miles
HC MAX 35 MEAS 35
CO MAX 0.30 MEAS 0.10
NO MAX 502 MEAS 75

It is a 95 318is everything stock and has 250 K miles on it -- transmission manual

how can there be such a huge difference in NO 75 vs 1144

Suggestions , ideas

Your nitrous oxide emissions increased at 25 MPH, not 25 miles, to clarify. I don't know who told you to drive around a lot before you went to get SMOG tested, but you want that engine as cold as possible when you go, so for what it's worth, I'd try to find another smog station that's much closer than 15 miles from your home.
Nevertheless, your data is pretty indicative of an aged Cat. You could always replace the Oxygen sensors if you inspect them and find them to be crusted white with carbon, but it's possible that you could actually read higher nitrous emissions once you get a more accurate (new/clean) sensor.
You can clean the throttle body and idle air control valve for free, but you're not in for a cheap fix.