Code 43 can mean either a problem with the oxygen sensor or a problem in the fuel supply system. The Helms manual says if the code is accompanied with poor driveability (sounds like this is the case) then it is indeed something in the fuel supply system.

Which of the following symptoms does the car have?

- Engine won't start
- Difficult to start engine
- Rough idle
- Misfire or rough running
- Fails emission test
- Loss of power
- Frequent stalling while warming up
- Frequent stalling after warming up

Sounds to me like you have "misfire or rough running" which would indicate (according to the Helms) something wrong with the fuel injectors.