So i think i know what the problem is but i just want some others input. Ive got a 99 civic ex and ive got a full exhaust, an aem cai, and a throttle body spacer. lately its been idling around 4 or 5 hundred and my speedometers been way off on the highway. is this because i havent had it tuned yet? or should i be looking at something else?

 

Is the CEL ON? if so, pull the code(s) from the ECU as detailed at the link in my signature. You may retrieve a code for the vehicle speed sensor, which sends the signal to the speedometer. The idle issue may be a tune problem, though you may want to try cleaning the IACV.

 

Nothing to do with a tune.
You don't need a tune for such minor modifications.
You can get one to squeeze a couple extra hp out of those modifications, but it's really not necessary and the car should run flawlessly without one with those minor modifications. Follow RonJ's advice.

 

ok yea my lights on but thats been on since i installed the header. and since the high flow cat and cat back every time ive gone to get it diagnosed it says something about the cat and the ics. so im thinking maybe the spacer is throwing that off but idk. its about a half inch, maybe even a 3/4 inch spacer. and when i installed the aftermarket cat i had to solder wire extensions because the o2 sensor was right against my shifting fork.

 

that's the whole root of the problem
there's something special about those wires that makes you unable to extend them like that. the only way to extend them is with a special o2 sensor extension wire

at least i'm pretty sure I read that somewhere

 

alright after doing some searching what I came up with is that you can't cut the wires between the sensor and the o2 sensor harness, you can have to cut the ones that are part of the engine wiring harness and extend those

did you cut the o2 sensors wires to extend it or did you extend the engine's wiring harness?

 

****, there were two spots to insert the o2 sensor and i had to move it to the other so i cut the wires of the sensor i think. i detached it and did it in my garage....i didnt know you couldnt do that. so what should i do?

 

can i just remove the wire i have now and replace it with that special o2 sensor wire?

 

take off the extra wire you added to the o2 sensor and make the o2 sensor's wires the lengths they were. Then try extending the engine harness side of the o2 wires and then plug it all in. Reset your ECU and see if the CEL comes back ever. If it doesn't come back, you were successful. If it ever comes back you will most likely need to replace the sensor so that it is completely intact.

 

i would just extend the engine harness portion of the o2 sensor wires.
how far did you extend the wires?