I've had this civic for a while. Just got around to clean it up and finish it to sell it but the idle keeps bobbing between 1k and 2k RPMS


At start up the idle is high then once it reach temp it start fluctuating. I've replaced the IACV, thermostat and flushed the coolant. The fan, heater and everything works like normal, and the temp gauge is where it should be.

Any ideas on where to go next?

 

Stock Civic?

CEL codes?

Have you tried adjusting the idle speed?

Have you bled the cooling system?

 

Yeah, stock civic. No codes. I bled the system today when I flushed the fluid and haven't adjusted the idle speed. Could that cause it to fluctuate? It runs a high idle until warm then fluctuates

 

Yes. See diagram in FAQs sticky.