emissions repair questions for an 87 5ktcs

[Dave Yentema]

Well first off, just wanted to say hi to all of you, as this is my first submission on here.

I've got an 87 5ktcs that i just went to take through inspection today, and it failed for CO. The standard is .5, and i failed with .56. The other numbers are 78 for HC (standard is 100) and 9.7 for CO2. I hav been trying to get this car inspected since december, when it failed for having a bad headlight. Since then everything has went wrong. 

I just had a 3in catback system done w/ a catco cat and summit race muffler, did a tune up a few months ago and for the most part the car runs great.  It does idle low every now and then, the inspection place documented my RPM at 727.

The car has no codes at all.

Any help would be awesome,

Dave