well its not my car but heres the deal. the car idles up and down like from 2500 on down to 1000. it was a 96 civic with a 96 LS motor runnin a hacked to **** 96 EX harness. it had about 5 engine codes. heres what i did. the owner didnt care how fast the car was so we put in a 98 DX motor. the problem still persists but now it only has 1 check engine light (2nd O2 sensor). sensor is hooked up too. still idles up and down like that. to my knowledge the motor has never been torn down. we even swapped in a 96-98 engine harness into it.
quick wrap::: so the final verdict is that the motor still idles up and down, this time with only 1 code. different motor, different harness, even tried a different ECU.

 

come on guys, help me out here.

 

check eacv. also o2 sensor could be bad