6 mos. ago I put a new Oxygen sensor in my '89 Honda CRX Si and that stopped my RPM's from surging up and down, but noiw the symptoms are back. As per this site's suggestion, I uninstalled my IACV, cleaned it and reinstalled it (Part looks brand new and was not dirty inside. Just had a bit of black dust accumulating on the screen). My RPM's still fluctuated between 900 RPM's and 3,000 RPM's. I bought a new Oxygen sensor and installed that too, but my RPM's continue to surge while in idle. Any other ideas as to what causes irradic idle?? Ty.

 

check to see if your car is equippted with a FCCV valve. it controls the idle when the engine is cold...

 

we just cleaned the IACV on my buddies car and it cleared up his erratic idle
im glad that fixed his cuz we weren't sure where to go from there...

do out cars have Throttle Position Sensor?

 

You need a new Throttle Position Sensor, had the same surging problem on my old 94 civic, cleared it right up.