94 Ranger, failed smog problem code 411

Recently I took my Ranger to be smogged and it failed miserably. I had a very high NO levels. I ran the codes and came up with 411 and 172 the first time I ran it. Since then 172 has gone away.

I was thinking I would do a tune up first and then try to get the 411 code to go away and then retest and see where I stand. Should I replace the IAC valve?

Also, I would really appreciate any other ideas on what may be causing the high NO levels. Thanks