i just swapped my 1990 civic dx engine for a 1992 civic si block and head, everything else is 1990 civic dx, and the car starts but the engine is always reving at 20 km per hour for about 5 seconds then it slows down at then it does it again, it does this aslong as the car is on, but what i dont under stand is when it does this the car is in neutral, and when i put it in gear, the speedometer goes higher, does anyone know whats wrong with the car??

 

this is what we call surging. it sounds like you have a vacum leak either in a hose or from your intake gasket. also coolant will cause this if your coolant level is low it will cause this and if you do not have the coolant running through your throttle body it will cause this

 

how can i find out which vacum hose has the leak, and also how can i tell if the coolant is running through the throttle body??

also i had to customize the wiring on the coolant temp sensor, if the wiring is wrong could it be the cause of the problem

the intake gasket is the one from the head, to the intake manifold right??

thanks for your help, and sorry to ask so many questions
Darryl