Power loss after engine warms up

[civic race]

I just purchased a 91 Civic hatchback and I am experiencing a power loss in all gears after the engine warms up. The power loss is only between 1000 and 3000 RPM then I get full torque. I’m thinking it is one of the sensors… but what one? Any help would be greatly appreciated.

 

[d-proff]

Any check engine lights

 

[civic race]

Yes, the check engine light comes on when the power loss starts. Also, if I turn off the engine and restart the power will return and the engine light will go off, but both will come back.

 

[d-proff]

Pull tht code may tell u ur problem

 

[civic race]

There were many codes, 1,4,8,16. I cleared the computer and now I only get #1. I believe that is the o2 sensor, but if the o2 sensor isn't working shouldn't I have a constant check engine light?

 

[civic race]

I changed the o2 sensor today and so far so good! thanks