One possibility is to replace the Engine Coolant Temperature (ECT) Sensor, which affects fuel injector pulse width. The ECT Sensor is a temperature dependent resistor (thermistor), whose resistance decreases as the engine coolant temperature increases. It provides a richer mixture when cold, leaner mixture when hot. They become corroded, due to not changing the coolant frequently enough, flood the engine, and waste a tremendous amount of fuel.
Here's what it looks like and costs:
http://www.autozone.com/autozone/cat...ext=ect+sensor
I'm not sure what engine you have, so your ECT Sensor may be slightly different.