i just finished my d15b swap. the engine starts right up, but idles at around 1800 rpms. after about 3 or 4 minutes it tries to idle down but keeps bouncing between 1000 and 1800 rpms. anyone have any ideas?
i cleared the codes and restarted it. the only code i am getting is 54 (CSF sensor) thanks for any help.

 

Code 54 is the CKF sensor which is an OBD2 only sensor. What ECU are you using with the D15B? What car is this? The CKF sensor is mounted down by the oil pump.

 

possible vacuum leak?

 

this is a 96 civic ex.( obd2) with an obd1 motor. i used the 96 intake manifold so that the sensors would work. but like you said its looking for a ckf sensor. could this cause the fast idle problem?