smog question

I have the '97 caravan 4cyl. and had a smog test today and it passed all except the NO (ppm) at 15mph, was just over the limit...It did pass the "NO" at 25 mph though..anything I should look for first..thanks

4 things come to mind:

1. The EGR passages are restricted.
2. A lean injector.
3. Carbon build up in the combustion chambers.
4. The O2 sensor is bad.

Seafoam is supposed to be good at cleaning engines for #3.

2,3,&4 are possiblities but not #1. The 4 cylinder didn't have an EGR system installed. Are you getting any symptoms besides being a smidge off on a smog test?

seems to run fine, was shocked when he told me it failed just that 1 item...All the other benchmarks were well below the max..