I've just aquired a clean '93 drop top with 2.3 dual spark, 117k mi. hiwaymileage is 23 mpg. is this normal? Can it be improved? Also car runs cold, temp gauge barely comes up. Also, are performance upgrades available for this engine and are they worth the trouble? Thanks  

If the engine isn't warming up to operating temperature, it might be running rich.  It is likely your thermostat is missing, is stuck open, opens early ,or has been replaced with a lower temperature version.  Fix that first and see if your mileage improves.  

just picked up new 195 deg. thermostat, and new air cleaner (needed) Will install this weekend. Thanks