Passed every category except for hydrocarbons. Car is bone stock on 91. The technician at the dealership, Tustin Mazda, didn't know what else could be the problem and obviously neither do I. Anyone know what it could be?

 

step 1: make sure the TPS is set right
step 2: make sure the ACV is working properly.

 

What where the numbers like?

 

Well it's too late now since I already had it "smogged" but I'll take a look when I get the chance

 

It's most likely your ECU. I am the original owner of a 90 GXL with 320K miles. Many years ago, I had trouble passing smog test in VA. I changed the ECU and passed with flying colors. Mazda did issue a TSB back in the early 90's about reprogramming the ECU for emissions.