What year is your Integra? Where did you get the information on the codes? I believe code 91 to be a problem with the fuel tank pressure sensor and not "Evaporative Emission Control System insufficient purge flow", like you suggested. The fuel tank pressure sensor converts fuel tank absolute pressure into electrical signals and inputs the ECM. Diagnostic trouble code 91 indicates either a high or low voltage problem in the Fuel Tank Pressure sensor. Probable causes would be either an open/short in the sensor circuit, the fuel tank pressure sensor itself or the ECM.

If you have a code 91 replacing the purge solenoid would be pointless. Replacing the purge solenoid for a code 90 on the other hand, may or not work depending on if it was defected in the first place.