I just installed a new exhaust from the header back with a test pipe and cat back...i reset my ecu because the check engine light came on when i moved the car with just the header on and when i drove it to my buddys shop (about40 miles) on an open header...now that i have everything on and reset the car at idle fluctuates from 1k to 2k and drops back to 1k and back up to 2k and keeps doing this...no CEL or any other issue..Any ideas..2000 Honda Civic si no swap still a b16a2

 

iacv? ficv? clean them and then try it.
check for vacuum leaks...
did you throw out an o2 sensor?

 

nope reused the second one replace the first one

 

clean your iacv or get a new one and clean the ficv under the TB.