mate i tune cars - and i'll let you know something...
your car cannot be remapped; it's too old. post '96 BMW's can be remapped, yours on the other hand will have to be 'chipped'. this involves removing the ECU, taking out the EEPROM chip and using a chip reader to obtain the information from your vehicle (fuel maps, ignition timing/advance, vanos, boost maps (if it's a turbo) and so forth). once that data has been gathered, the file can be modified and re-written on a NEW chip that will go back into your ecu. that's the only headache with older cars; it takes a bit longer, but the result is still the same.
if you drive the car 'nicely' - you'll definitely notice an increase in MPG - but, as somebody already suggested, it might be an idea to check your car on a diagnostic machine because if things like your lambda sensors are going duff, you'll be wasting petrol if the car isn't running nicely!
hope that helps - pm me if you need help, i've gotta go fit some angel eyes *grunts*