I have a 2000 civic ex. It drives perfectly fine other than a high idle (2000 then down to 1500 then to 1100rpms) until the engine warms up. Once the engine warms up the idle returns to about 1500 rpms and it hesitates when i try to accelerate. It also "jumps back" when i let off the gas. I have gotten the codes read at autozone and it came back with a misfire in 1 of the cylinders, bad o2 sensor, and iat or iac sensor (cant remember which it was). the o2 sensor on the manifold is there but is not plugged in and dont see where it should be plugged into here's a pic of the plug

 

its supposed to be connected by the distributor i think im not sure what exactly im looking at but replace your o2 sensor and then change out spark plugs and ignition wires and you should be good unless your misfire is coming from low compression in cylinder 1 or possible bent valves but i think its your plugs and wires

 

the plug that's not plugged in is the o2 sensor plug

 

okay so there you go then you need plug that in and it should fix your problem if not change out the plugs and wires

 

Definitely plug in the O2 sensor. Then reset the ECU to clear the CEL codes, drive the car, and then pull the codes again at home using the jumper wire method. Post all codes that you retrieve.

 

thats what im saying their is nothing to plug it into.. never was when i bought the car.. so i need a whole new wire harness?

 

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i highly doubt its the plugs and wires as someone stated above wait until its dark start your car open your hood and if you can see them arching (sparks jumping from wire to wire) then change them if not then dont bother

and im sre you know how to check plugs