Ok this is a crx si intake manifold and i disconnect the iac with the car off like the manual says then turn it on and raise the idle then turn car off and reconnect iac. After sometimes only a day its back down to 500 rpm and sometimes below that cause the car to vibrate. why do i keep losing rpms.

also is there a chance that my tach could be off and that i should set it to maybe 1000rpms? Assuming i get the other problem fixed

 

After you set the idle and turned the car off and replugged the IAC, did you remember to pull the red Hazard fuse (in the engine fuse box) for 30 or so seconds to reset the ECU?

If that's not the answer, the be sure to clean the screens on the IAC, then do it again, but make sure the car has idled long enough for the cooling fan to kick on once and turn itself back off.

 

Check for a vacuum leak .