one is stuck on my old manifold and the other was never on how can this affect the motor?

As I have just learned this greatly impacts fuel economy. The ECU isn't getting the right reading of oxygen concentration, and is thus mis-regulating the fuel output. Also, if your air-fuel ratio isn't at 14.7:1, which it isn't if you have faulty (or missing) O2 sensors, you'll be losing power.

poor throttle response and poor fuel economy.