Civic Wagon 1990
D16z6 swap
converted MPFI
obd0-1 ECU jumper harness
P28 ECU

It seems to come and go. High idle on start at ~1.7k rpm will eventually lower to a 7-800 rpm. surges are apparently occurring most often after warmup. not a constant issue

I was going to next replace my booster. brakes do not work that well even after full system flush. No signs of leakage from master cylinder. Sometimes when I pump the brake pedal my idle will rise, to me what seems significantly.

I have attempted to solve a surging idle by the following various fixes.

-Cleaned IACV
-Replaced IACV with different/used IACV
-Replace IACV o-ring

-Clean throttle body
-Replace TB gasket
-Install new OEM FITV

-Clean intake manifold
-Replace manifold gasket
-Replace booster <-> manifold vacuum check valve
-All vacuum lines connected, PCV and charcoal canister

-Bled coolant properly. fan comes on and t-stat open
-Replace ECT switch with different/used switch