Rep Power: 0

I recently had a new d16y8 put in in my 98 ex coupe, along with a new clutch and rebuilt trans. The car has ran fine for the most part, never left me stranded, took it on a long road trip as well. But since i’ve had it it doesn’t stay at 1,000 rpm. its usually 500-1,000. I’ve had the IACV replaced as well as the throttle body and its still had the same problem.

 
Rep Power: 209

normal operating temp idle is 750 +/- rpms. Cold start idle is around 1000 rpms for the first few minutes. This may help: https://honda-tech.com/forums/honda-...rm-up-3207863/

Test always before throwing parts at it. Remove PCV valve and shake it...if it ratlles it's working, if it doesn't rattle replace it or spray it out with brake cleaner to remove soot.

If you do a compression test make sure to do a dry and wet (two teaspoons of oil in cylinder) to get proper reading. Also, if you do a compression test do it while battery is fully charged and charging during test, gas pedal fully depressed (WOT) to prevent gas from entering cylinders. Additionally, can disconnect distributor harness to prevent spark. Allow engine to crank a few seconds past peak psi reading to ensure consistency of test and to monitor psi drop off after peak psi.

Other possibilities:
air bubbles in coolant
engine/chassis grounds
clogged catalytic converter
o2 sensor weak
tps