Took my '92 Protege to get emissions inspection. Failed b/c hc was high at 196 and CO% was 4.48 but legal limit is 0.61. I just changed my oil so that shouldn't be the problem. Any ideas as to why the CO was so high? Shop wants to charge $100 for diagnostics...

 

You can get high CO from a rich A/F mixture. It could be a mechanical issue(leaky injectors or something else) or it could be as simple as someone was not maintaining it over the years. Is it throwing a code with the MIL on? Where is B/C cat, before or behind the cat? Use pre or post cat to ID the location. Just an FYI!
My suggestion: pay the $100 to a reputable shop giving the idea that you will have them fix it. Get the list of problems and walk. IF YOU ARE NOT SURE HOW TO FIX THE PROBLEMS, let them fix it. You can spend cash on parts and put them in wrong, and then just have to pay the shop to fix it anyway.