I have a 98 Civic EX with a B18C GSR swap and the car is misfiring when is idling. Also, when the engine is warmed up, at idle the rpm tends to drop to 500 or so almost seems like it would cause the car to stall, but after the drop the car would rev back up to 1000 then it drops again. There is no CEL, and I changed the Spark plugs on it a few days ago is still having the same problem. Does anyone know how I can fix this problem? Thanks

 

rebuild the motor, could have low compression

 

ya good advice....OP what is your fuel pressue at idle ? have you done an injector pulse test when at idle is you ign timing on ?