i have a 92 civic si 1.6 vtec and the car has a bad idle up down up down. no check engine light, recently i replaced the thermostat and changed the IAC valve but i got the part at a junk yard. And the concern is still there. Is there anything elso i should check?? i need to pass smog!!!! HELP ME

 

clean the iacv if you haven't , check for vacum leaks, and check your tps, or sometimes even a layer of carbon can build up on the throttle body and get stuck a little open

 

i already cleand the Iac i just got some carb cleaner and cleand it out. but now that you mention my throttle body i used this chemtool 3 step fuel system cleaner and i remember that one of the steps was to spray some **** in the manifold maybe something got stuck in there?? you think that might be the problem?? HMMM

 

Clean the fast idle thermo valve (fitv), under the throttle body

 

have you gone thru the idle adj procedure...warm car up turn off disconect the iac valve start up adj to 600-700 with adj screw turn off reconect iac and restart