Ok this only happens on night time, I guess it has to do something with the cold temp but its weard. I turn on the car and the idle is fine then after I start driving and make a complete stop at a red light and neutral my idle goes 1k to 1250 and its constant up and down. But I also found out that if I let go of the brake pedal while I am waiting for the light to go green it stops and goes normal I just put on the e-brake so the car wont roll back or forth. I hate this **** and going to replace it if I can get one.

I MIGHT BUY ONE IF SOMEONE HAS AN EXTRA ONE.

 

My IACV was doing that to me until I repolaced it.

 

happened to me after i tried to use intake cleaner until i properly adjusted my idle properly. at idle, youre somehow letting in more air past the TB, so the ECU tries to cut it, and then just keeps repeating the cycle. it can be fixed with adjusting the idle by following the factory procedures which includes resetting the ecu.

 

sounds like it to me

 

IACV or Vacuum

 

My 1G CRX Si did the same thing. Only under certain circumstances though.
Never did figure it out. Then it got totaled.
Seemed to be a common problem on 85-86 CRX Si's and Civic Si's
I never did check IACV, though.
Is yours a 3G civic/ 1G crx?