Hey everyone
I have 98 civic dx with a freshly rebuilt JDM GSR motor. I have roughly 4k miles on the motor.
My motor setup consists of 82mm bore block with ITR pistons on stock gsr rods, CTR cams, S2 intake manifold, and tri-y headers. The motor is currently running a stock obd2a JDM ITR ecu.
The motor starts up perfectly and idles GREAT. But after driving for about 40 minutes, my idle starts acting funny. It would dip really low and sometimes stall when I'm in neutral. When I'm driving and decelerate while in gear, it would have like a little tug. Does anyone have an explanation to the cause of this? Any input would be greatly appreciated.

 

Have you tried adjusting your idle control screw on the throttle body?
Maybe you need to hit that sweet spot.
Make sure it's completely warmed up when you do this.
It's also possible moving the screw will do nothing unless you jump the ecu but it's worth a try.

 

This.