Bought a 99 civic with a b18a1 swap. When it's cold the idle will raise from 800 up to 1800, then back down again. This will continue repeating until the engine is slightly warm (just above C).

I have cleaned the iacv, and the fitv. Both looked new.

Have also checked for vacuum leaks, no issues.

 

Clean doesn't fix broken or out of proper adjustment.
Crank the car up cold. Place your finger over the lower hole inside the mouth of the throttle body (at the 8 o'clock position). If the idle stabilizes, then your problem is the FITV. Repair or replace as necessary.

 

Tried that, idle still fluctuates. Might need a new IACV, not 100% how to test it.
​​​​​​Ive tried warming up the car and plugging the IACV and FITV hole, causing the car to almost die but not completely.

The fluctuations only happen when at a stand still. A bit of throttle, or clutch engagement and it goes away.