Look at the tuneup/emission label in the engine compartment and list the codes. In particular I am interested if it has an oxidizing catalyst (OC) or a three way catalyst (TWC). Also, does your car have O2 sensor(s) and EGR?

I expect your car is pre TWC/O2 sensor in which case it would have an OC and a full time air pump, no O2 sensor(s), and maybe EGR.

I need to understand the emission control architecture before I can offer a useful diagnosis of the test data.

I am assuming that this car is either a US or CA model (stated on the above referenced label) and NOT a gray market car. Is this correct?

Do you have any previous emission test data?

Does anything in the engine compartment appear to be jerry-rigged?

Fuel tank cap holding pressure has nothing to do with tailpipe HC readings.

My hunch is that the high HC readings with everything else okay are due to misfires, which points to the ignition system, but I'd like more information.

Duke