I've went thru and seached the forums on this topic, but haven't been able to find a cure for my problem. I've got a 1997 Civic Hatch DX that I just replaced the stock 1.6L engine with another stock 1.6L engine. After I got everything done I fired it up and it started and seemed to run really smooth. Once the engine had warmed up it began surging up & down at idle. It would go from ~800 to 1500 RPM over and over again. When I gave it some gas it smoothed out and the problem went away. I don't notice it when I am driving, just in park while the car is idling??? Does anyone have any ideas? I pulled the IAC sensor off and let it run without it and it seemed to steady for a while, but then the surging came back.

Thanks,
Chad

 

Yeah I'm having the same issure, keep an eye on my thread. Run through the checklist I have put up and let me know if any of those things solve the issue