Over the past month my fuel economy has plummeted to around 7 mpg. If I hit the gas halfway, the car won't really accelerate. If I hit it 3/4 throttle, it will accelerate.

Sometimes after the car is warmed up and I've been driving for around 20 minutes, the car will drive perfectly fine.

o2 sensor??

 

Do ur normal fuel efficiency check list.
1. Tire pressure
2.spark plugs
3. Wires
4. Fuel filter
5. O2 sensor
6. Oil change
7. Air filter

If nothing works...
You might need to get your injectors serviced and or check for leaks as well as check your fuel pump.

 

Thanks. I'm installing the o2 sensor and fuel filter this weekend. I replaced the fuel filter 25k miles ago or so. I've never replaced the o2 sensor and I've put around 70k on the car since 2003...

 

you could also check for proper operation/voltage of the TPS.