Engine Problems

[civic_SI_hatch]

i'm swaping a 99 civic si ... i'm using my old harness and ecu of the 92 si hatch ... it cranks but revs up and down a little... what could be the problem? also the check engine light comes on? is it suppose to?

 

[slammedb18acivic]

revs up and down like . goes up to 3 grand and back down to 1000 rpms. if so you have a vaccum leak or a bad coolant sensor. if you changed any gaskets when you did the swap such as the intake manifold go back and loosen it up and tighten them evenly . bad sensors can be, throttle position sensor ,idle air control, or fast idle valve .

 

[E_SolSi]

what ECU are you using?

 

[civic_SI_hatch]

i'm using the stock ecu from the 92 civic si hatch... i think its a p28.. but i'm not sure